At present, the parent fund of mainstream stock grading funds can be raised by off-site and on-site means. After the establishment of the fund, the parent fund subscribed by investors in the market is divided into A share and B share, which are listed and traded (Shenzhen Stock Exchange model). Usually, the parent fund can only purchase and redeem, but can't trade (Shanghai Stock Exchange can trade), while A and B shares can only be listed and traded, but can't be redeemed. Because A and B are separated from the parent fund, according to the fund trading rules, investors can buy the same number of A and B shares from the secondary market and merge them into the parent fund for redemption. You can also go to the fund company to buy the parent fund first, and then go to the secondary market to split it into the same share of A and B. This is called subscription split. Because A and B shares are traded in the exchange market, the transaction price is determined by the relationship between supply and demand, which may deviate from the net value and there is a discount premium. When the discount premium reaches a certain range, investors can arbitrage.