Under the condition of non-steady flow, the obtaining of hydrogeological parameters through pumping test with straight recharge boundary involves the transcendental equation of 3 (boundary direction known, position unknown) or 4 (both boundary direction and position unknown) unknowns, which could not be solved by conventional analytical methods. The existing methods, including method of specific standard curve comparison, method of inflection point, simplified algorithm, nonlinear least square method and binary linear regression method, are inconvenient for practical engineering as they are dependent on graph with complicated calculation process, limited application range and big calculation error. In this article, optimization fitting method was employed to adapt to the engineering parameter range, and the substitution of simple function for the Theis well function of non-steady flow was carried out. Furthermore, a simplified analytic expression for the parameters was obtained by summarizing the drawdown ratio formulas. The calculation process is simple and convenient for practical use.