The model used for analyzing the gain characteristics of Er-Yb–doped phosphate glass waveguide amplifier (EYDWA) with forward-backward pumped configuration (FBPC) is based on the rate and optical power propagation equations, which include forward-backward pump, upconversion mechanisms, and light propagation loss. An overlap factor, which considers the difference between signal and pump field intensity distribution in channel waveguides, is introduced to evaluate the gain of EYDWA. The results show that FBPC can make the pump power light more uniform and lower than that in forward-pumped configuration (FPC), inhibiting the upconversion. Thus, FBPC increases the gain of the device by 2 to 3 dB compared with FPC, and pump conversion efficiency (PCE) is accordingly raised by 50%. The total power of amplified spontaneous emission (ASE) is also higher than that in FPC. The gain of EYDWA is affected obviously by the pump configuration, modes of pump light, upconversion coefficient, and scattering loss. Moreover the detrimental effect due to the above factors is reduced by the FBPC.