Abstract: An adaptive step-size method for the coupled equations of multi-pumped broadband Raman amplifiers was proposed based on Runge-Kutta-Fehlberg methods.This algorithm adjusts the step-size appropriately according to the presupposed precision and the local truncation error of each step.Simulation results indicate that our adaptive step-size method improves the accuracy and the simulating speed efficiently compared with other traditional algorithms and suits the numerical simulation for fiber Raman amplifier.