The model used for analyzing the gain characteristics of Erdoped waveguide amplifier （EDWA） is based on the ratepropagation equations with intensity profiles of pump and signal light. The intensity profiles of pump and signal light for different channel opening width （DCOW） of Erdoped waveguide is discussed. And the numerical method （NM） considering the difference of intensity profiles between signal and pump light in channel waveguide with DCOW is used to solve the gain characteristics of signal light in EDWA. An overlap factor Γsp between light intensity profiles of signal and pump is introduced to modify the conventional simplified method （CSM） in EDWA, which is a revised version of the conventional simplified method （RCSM）. Results show that difference of 297 dB in gain for -10 dBm signal light at 1534 nm due to DCOW of waveguides is obtained for a 4 cm long waveguide amplifier pumped by 80 mw at 980 nm. Comparing with CSM, the gain characteristics of EDWA from RCSM is simpler and better approaches the result from NM. Therefore, the RCSM is valuable in the research of EDWA.