Objective: To observe the difference of biological effects on canine bladder by Nd:YAP laser with different power and different irradiation time. Methods: The canine bladder was irradiated with different power and different irradiation time. The effects of ablation and thermal coagulation in different laser settings were observed. The damage scale was evaluated macroscopically, with microscope and with electroscope. Results: The thermal coagulation effects is mostly and ablation effects is subordinate on the canine bladder by irradiation of Nd:YAP laser on. Pathology vision shows the thermal coagulation dose on perforation is 10W, 6s, 20W, 4s; 30W, 3s; 40W, 2s; 50-60W, 1s; the dose of whole audience wear through is 10W, 6s; 20W, 4s; 30W, 3s; 40W, 2s; 50-60W, 1s. Conclusions: The thermal coagulation effects is mostly and ablation effects is subordinate on biological effect of Nd:YAP laser on canine bladder. The better safety dose is power 10W, duration time less than 6s; power 20W, duration time less than 4s. power 30W, time less than 3s. power 40W, time less than 2s. The ablation and thermal coagulation effects of Nd:YAP laser on canine bladder is homocercal of power and time.