The simulation model of a ring Er-doped fiber laser based on chirped phase shifted fiber Bragg grating (CPSFBG) is researched. The transmission spectrum of CPSFBG is obtained through transmission matrix method and traveling wave rate equation is performed numerically to obtain Er-doped fiber up-level particle number, output laser power time domain variation and output laser spectrum during laser operation. The pumping source with 0.3 W power and 980 nm is used to obtain the continuous laser output with 0.078 W output and 0.02 nm bandwidth. The output laser power linearly changing with the ratio of pumping power and output coupling is analyzed in detail. Simulation results show that output laser power changes linearly with pumping laser power and there is an optimal output coupling ratio to realize the maximum laser power.