Laser speckle is one of the main sources of noise in the measurement process of laser triangulation measurement, which significantly impacts the measurement uncertainty of triangulation measurement instruments. A triangulation measurement device taking two lasers with different wavelengths as the light sources is proposed to suppress the speckle phenomenon during testing and improve the measurement accuracy of the instrument. At first, the working principle of laser triangulation measurement and the relationship between speckle and the measurement uncertainty of the device are introduced. And then, the principle of using dual-wavelength illumination to suppress speckle and improve the accuracy of triangulation measurements is introduced, and the speckle suppression effects under different power ratios of light sources are analyzed. At last, lasers with wavelengths of 405 nm and 420 nm are used to conduct triangulation measurement experiment. Experimental results indicate that the method can reduce the measurement uncertainty of the theodolite. After illumination with a dual-wavelength light source, the instrument's testing uncertainty decreases from 0.52 μm to 0.23 μm. The measurement uncertainty can be reduced, which lays the technical groundwork for the development of higher precision laser triangulation instruments and possesses important practical value.