An analytical model of cw longitudinally diode-pumped Er３＋,Yb３＋ co-doped phosphate glass lasers that includes the influence of cooperative upconversion and cumulative energy transfer effects has been developed. The results of general output modeling were applied to a laser with Gaussian beams, and numerical calculation has been made to study the influence of cooperative upconversion and cumulative energy transfer effects, where the dependence of laser output on the influence of cooperative upconversion and cumulative energy transfer effects was investigated in particular. Especially, we find that the influence of cooperative upconversion on the threshold can be up to 22%. The model is in good agreement with measurements of the laser in a plane-plane cavity. Further numerical analysis will be developed.Our results are useful for optimizing the parameters of this kind of lasers.