According to the nature of the parent fund, it can be divided into two categories. One type of parent fund is an index fund, and every three parent funds can be divided into 1 1 double-empty shares and two or more times shares according to the ratio of 1:2, or every four parent funds can be divided into 1 double-empty shares and three or more times shares. Another kind of parent fund is the money fund, which is divided into two times more shares and two times equal empty shares, or every three parent funds are divided into two times more empty shares 1 and 1, which can be regarded as low-leverage mini stock index futures. Long-short graded fund is a kind of graded fund. It is a hierarchical fund that decomposes the parent fund into bullish and bearish shares through structural decomposition.