Generally speaking, there are three social security systems in the world at present, one is DB pay-as-you-go system, the other is DC full accumulation system, and finally there are various mixed models, such as semi-accumulation system and nominal account. The second DC-type complete accumulation system has two forms. One is the Chilean model, which has been adopted by nearly ten Latin American countries. Personal payment is entirely in personal account. The state provides several investment funds, and individuals decide the investment portfolio. The fund manager is responsible for the specific operation, and the loss is borne by the individual. The state does not assume any responsibility. The future pension payment level depends almost entirely on the payment balance and investment income (minus management fees). This is a "defined contribution type". Therefore, under the Chilean model, the state does not have a central social security fund. The so-called social security fund is scattered in everyone's account. Investment decision is a personal behavior and a decentralized decision. Personal decisions are made according to personal preferences and the type of investment funds provided by the state. Generally speaking, from the perspective of risk and interest rate, there are five or six kinds of investment funds to choose from, for example, non-trading short-term government bond funds (G funds), bond market funds (F funds), ordinary stock funds (C funds), small capitalization stock index investment funds (S funds), international stock index funds (I funds) and so on. Regarding the establishment of investment funds, although the situation in different countries is not the same, it is almost the same.

The second is the "central provident fund system". This kind of social security fund is characterized by DC-style pension payment, and its rate of return is determined by the state according to the investment income, but the fund investment is completely operated by the state. Therefore, under this system, there is a certain relationship between the final payment of pension and the accumulation of previous contributions, but this relationship is not entirely actuarial, because the return on investment is "regulated" and "managed" by the state. About ten former British colonial countries have adopted this model. They invested a small part (about 15% or less) in the stock market, and most of them invested in infrastructure in the form of purchasing government bonds, resulting in poor returns and large losses. The third is the hybrid type. Mixed social security system can also be basically divided into two categories: one is semi-accumulation system, which consists of two parts, one is pay-as-you-go system, and the other is accumulation system. For countries that implement semi-accumulation system, the details of the specific system are also very different, but generally it is the part of funds held by the state and the pay-as-you-go system is implemented. Theoretically, the design framework of China's current social security system is semi-cumulative. The three reform plans put forward by the United States all belong to this typical semi-accumulation system. The other is "nominal payment determination", also known as "nominal account system", which is a combination of DB and DC. It has the advantages of both the pay-as-you-go system and the accumulation system, that is, the former financing method is used to pay the current retired generation with the contribution of contemporary employees, thus avoiding the transition cost from the pay-as-you-go system to the accumulation system, but in terms of payment, it is payment-oriented. In recent years, six countries in Europe and Asia have taken the lead in adopting this brand-new system, which is very attractive to some countries in transition. In the nominal account system adopted by six countries in Europe and Asia, some countries completely control the social security fund by the central government, while others divide it into two parts, one part is invested by the state as a whole, and the other part is allocated to individual accounts, leaving it to individual investment decisions.