Four levels of the difficulty of the distributive law of multiplication are established (including the operational memory level, the conceptual memory level, the explanatory understanding level and the exploratory understanding level). Based on this, this paper makes a comparative analysis of the exercises of the distributive law of multiplication in the six editions of the textbooks. The conclusions are as follows: The total amount of exercises in different textbooks varies greatly, the amount and proportion of exercises at the same level vary greatly. And in light of that, it is necessary to establish difficulty classification standards for exercises research and carefully consider the total quantity and the number of exercises of different levels. Meanwhile, teachers should add and subtract exercises of different levels according to the learning conditions.