Lanthanum crown glass has attracted much attention in the application field of car glass because of its excellent mechanical properties. A three-point bending strength tester was used to test and comparatively analyze the bending strength of the car glass samples before and after polishing, aiming to investigate the impact of surface roughness on its three-point bending strength. The results showed that the average bending strength of samples post surface polishing treatment increased by 9.4 MPa compared to the untreated samples, and the results exhibited great stability. Furthermore, by using numerical analysis methods to compare the mean values derived from the raw data, 90% confidence interval and 80% confidence interval, it is found that the 80% confidence interval can effectively remove outliers and accurately reflect the bending strength values of the samples.