With the expansion of power system scale, higher requirements are imposed on convergence and calculation speed of power flow algorithm. Therefore, a retaining-nonlinearity flow algorithm based on current-influx model with optimal multiplier is proposed. According to the characteristics of the power flow equations in rectangular coordinate, a method for calculating the optimal multiplier is given firstly. This method only needs to solve a unary cubic equation without adding any additional calculations. On this basis, the optimal multiplier is applied to the retaining-nonlinearity flow algorithm based on current-influx model. In iterative process of power flow calculation, the optimal multiplier is used to adjust the voltage correction. The convergence reliability and convergence speed of power flow calculation are improved. Numerical examples show that the proposed method can ensure that the system flow is non-divergent when the flow equation has no solution, and can improve the calculation speed when the flow equation has a solution. This work is supported by Project of Liaoning Education Department (No. JFL201715401).