Abstract: The function expression of the rain intensity- polarimetric phase shift model is complex, making it difficult to derive an analytical expression for inverting the rainfall intensity. Simulated annealing is an effective method for inverting rain intensity, but it is computationally time-consuming. In response to this problem, a rain intensity inversion algorithm based on the bisection method is proposed. Firstly, the rain intensity inversion problem is transformed into a function zero-point solving problem. Then, the bisection method is employed for model calculation, and a rain intensity inversion algorithm based on the bisection method is presented. Finally, the efficiency of the new algorithm is verified through simulation experiments. The results show that compared with the simulated annealing algorithm, the bisection method can significantly improve the inversion efficiency while ensuring the inversion accuracy, reducing the average required time for each inversion by about 75%.