To meet the requirement of the collinearity of laser beams during thickness measurements, a vision detection method for sensor optical axis position is proposed based on a double-splitting prism.According to the light propagation path and spot variation rules of a single laser beam in two spectroscopic prisms, the mathematical model between the relative positions of the two lasers and the spot centers is constructed according to the spectroscope coordinate system. With the help of the conversion relationship between the prism coordinate system and image coordinate system, the relative positions of the laser beams can be quickly calculated using the four fitting spot center coordinates, which can convert the collinearity measurement of the laser beam into the fitting and provides a comparison of spot center coordinates.The experimental results show that using the proposed method, the maximumangle between the two laser beams is 0.17°, and the maximum distance is 0.05 mm in the measuring range.Under these conditions,the measurement of the gauge block before and after adjustment shows that the thickness measurement error is reduced from 12 μm to 4 μm, which indirectly verifies the effectiveness of the collinear detection method.The proposed method realizes digitalization and visualization in the laser beam adjustment process, enables metrological traceability of the measurement results, and helps to quantitatively analyze the thickness measurement errors caused by the non-coincidence of the measuring lines of the two laser sensors.