For domestic futures, the most frequent monthly change of main contracts is about 1 time, such as non-ferrous metals and crude oil. Most other varieties change their monthly contracts in June, May and September in turn, and some varieties change their monthly contracts in June, May and June in turn (such as apples and June). Sometimes, some varieties encounter big market, which leads to active trading, such as non-ferrous metals and crude oil, but most of them skip a certain month and go directly to the next month of that month. To give a simple example, under normal circumstances, the contract of a certain variety rotates in June, May and September in turn, but when it encounters a unilateral big market, the contract changes from May to June, and it changes to July after about 1 month, which is probably the case. In July, the situation of skipping August and directly changing to September is likely to be whether speculative funds will suddenly reverse in the game market. However, because 1, 5 and 9 contracts are the traditional active months of this variety, there are already a certain number of open contracts or positions in advance, which leads to the situation of changing months.