Microchip solid-state laser is an important light source for precision measuring instruments because of its small size and long life. The plano-plano and half-external cavity Nd:YAG and Nd:YVO₄ microchip lasers were constructed. The length of the laser resonator was changed by controlling the expansion and contraction of the piezoelectric ceramics. At the same time, the longitudinal mode and wavelength were observed by using F-P scanning interferometer and wavemeter. The cavity tuning characteristics of the two microchip solid-state lasers were studied, including the relationship between the cavity length and the optical power, the optical power and the variation rules of single and double longitudinal modes in the process of laser longitudinal mode sweeping through the laser output bandwidth. The experimental results show that the single and double longitudinal modes appear alternately during the process of cavity tuning, and the cavity length and pump current jointly affect the output mode and optical power of the laser.