Novel theoretical model based on rate equations considering re-absorption is set up to deal with the output characteristics of continuous wave (CW) Tm: YAP laser for the first time. Compared with the model that ignore the reabsorption of thulium ion at all (Model 1) or only takes it as a fixed loss (Model 2), the simulation results of the new model (Model 3) can reflect the entire process of reabsorption more accurately and obtain numerical simulation results that are closer to experimental results. Laser characteristics of LD end-pumped CW Tm: YAP crystal is achieved experimentally, which can demonstrate the accuracy of the model. Output power of 7.1 W at 1936 nm is obtained with resonator length of 78 mm under the incident pump power of 27.13 W. While the simulation results on output power of Tm: YAP laser under incident pump power of 27.13 W and cavity length of 78 mm are 17.2 W, 2.76 W, 7.36 W for Model 1, 2, 3. The finding indicates that the new model can evaluate the output performance of Tm: YAP lasers in precise.