The related knowledge points of equivalent substitution in primary school mathematics are: the nature of equality, equivalent substitution method, addition, subtraction and elimination method. Among them, the equivalent substitution method means that a quantity is replaced by an equivalent quantity, which is a basic thinking method in mathematics and the basis of algebraic thinking method. The idea of equivalent substitution in a narrow sense is embodied in the nature of equality, that is, the transitivity of equality: if a = b and b = c, then a = C.