High-quality Er,Pr:YAP crystals with two different Pr³⁺ concentrations are grown successfully, and the spectra and laser performances are studied in contrast. Both two crystals exhibit a wide absorption band with a central wavelength at 972 nm and high transmittance of over 80% in the wavelength range of 2.5 to 5 μm. The luminescence and laser properties are improved when the concentration of Pr³⁺ decreased from 0.2 at% to 0.1 at%. The maximum powers of 1040 and 835 mW are achieved in the Er,0.1Pr:YAP, and Er,0.2Pr:YAP crystals, corresponding to slope efficiencies of 13.97% and 10.94%, respectively. All the results indicate that co-doping with an appropriate concentration of deactivating Pr³⁺ is an effective method to attenuate the self-termination effect of Er³⁺, and then further improve the laser performance.