The amount of the calculation of an algorithm may be expressed by the number of multiplication and addition operations (one division is treated as a multiplication,one subtraction treated as an addition).A multiplication or an addition operation is called a flop,i.e.,a floating-point operation.This is the first of three serial papers 'Computational efficiency of the identification methods',which focuses on the computational efficiency of the recursive algorithms,including the flops of the vector and matrix operations,and the minimum flops of the stochastic gradient identification algorithm,the least squares identification algorithm,the recursive least squares identification algorithm for linear regression systems,multivariate linear regression systems and multivariable systems.