A method of optimizing the stability of the resonant cavity by adding an additional crystal into the laser resonant cavity is studied for the first time. The laser performance can be effectively improved by adding crystals with appropriate refractive index into the resonant cavity. In this study, a Nd3+∶Gd0.1Y0.9AlO3 (Nd∶GYAP) crystal laser device was built, and LBO crystal were added into the resonant cavity. The effects of LBO crystal on the laser properties of b-cut and c-cut crystals were compared respectively. The laser performance with and without LBO crystal was characterized in terms of output power, laser wavelength, beam quality and polarization characteristics. When LBO crystal is inserted into the laser resonant cavity, the slope efficiency of b-cut Nd∶GYAP increases from 18.9% to 24.3%, and that of c-cut Nd∶GYAP increases from 2.87% to 10.07% without changing the spectrum and beam quality. The maximum output power of b-cut crystal increases from 0.931 W to 1.254 W, and that of c-cut crystal increases from 63 mW to 134 mW. However, the polarization of the output laser deflects to some extent due to the optical rotation effect. This research provides a way to improve the slope efficiency and output power of lasers in the cases of the cavity length must be extended such as tuning and mode-locking operations.