The optimum fitting method was used to make an alternative of Theis well function represented with series in an adaptive engineering parameters range. According to the selected points on the drawdown-time relationship curve of the pumping test, the drawdown ratio method was adopted to derivate the function of discontinuous step pumping flow, and obtain the solution of the quadratic equation in one unknown for hydroge - ological parameters. The accuracy analysis show that the maximum relative error is less than 2% in the engineering application parameters, which can meet the requirement for the calculation accuracy in the actual engineering application.