Using by different output transmittances of 2%, 5%, and 10%, we have investigated the continuously tunable laser performance of c-cut Tm:YAP crystal. The 5-mm long c-cut crystal with 4 at.% thulium ion was used. Without a tuning element, the slope efficiency respect to the absorbed pump power reached 44.1% with transmittance of 5%, corresponding to the conversion efficiency of 35.3%. The laser operated at TEM00 mode with a beam quality factor of M2 ~ 1.3, which was demonstrated by a 90/10 knife-edge method. A 3-mm thick birefringent plate was used as a tuning element. At transmittance of 5%, the widest tunable range of 159 nm extended from 1899 to 2058 nm. For transmittances of 2% and 10%, the tunable ranges of 150 and 68 nm were achieved, respectively.