In this paper, a quasi-common-path method to improve the stability of laser measurement instruments is proposed. The method releases the strictness of the common-path structure and enables the compensation of errors caused by air turbulence. A wavefront measurement system is set up to simultaneously detect both the wavefronts of the quasi-common-path beams, of which the orthogonal distance varies from 0 to 4 times the beam diameter. The correlation coefficient between two wavefronts remains around 0.9 in turbulence, which verifies the feasibility. Based on the method, a three-axis interferometer whose measuring optical paths orthogonally split 30 mm is established, and the stability of the optical paths is evaluated. The standard deviations of the displacement and the displacement difference at the original point are about 0.31 μm and 0.006 μm, respectively, while these performance properties at 1 m are 1.14 μm and 0.02 μm, respectively. The experimental results show that quasi-common-path beams allow for stability improvement, which can also be widely used in the field of precision machine manufacturing.