Objective To study a detection method of grating scalar lines in stereoscopic printing. Methods First, a lenticular grating was fixed on the test platform. The base of a probe moved along the horizontal direction, and at the same time the terminals of the probe always kept contacting with the surface of the lenticular grating in the vertical direction. Then the horizontal and vertical displacements of the probe were acquired by a computer in real time and the displacements data were saved to the database. The measured curve of the lenticular grating surface was displayed on a computer screen. Finally the horizontal and vertical displacements of the probe were substituted into the data processing algorithm and the line number of the tested grating was calculated. Results A lenticular grating with 100 lines was measured by this method as a test grating. The experimental results showed that the number of lines tested by this new method was very close to the number of lines tested by the traditional method and the test could be finished within 60 seconds. Conclusion The error of the traditional artificial measurement was avoided in the new method and the test time was reduced to 60 seconds from 300 seconds. The method showed the advantages of high efficiency, high stability and high reliability.