The optical lever method is one of the substrate curvature-based instrumentations, which has been widely used to measure the residual stress of thin films. In this work, the Ti and TiN films were prepared based on SUS304 substrate by arc with different thicknesses, and the morphology, density and phase of two films were studied. Curvature radius of the substrate before and after coating was measured by the optical lever method from the front side (positive test method) and the opposite side (negative test method). The residual stresses of films were calculated via Stoney method. The test error and the applicable scope of the negative test method were studied by comparing the results of the positive and negative test methods and the morphology, density, and crystal structure of the films. The results show that the measurement value of residual stress by the negative testmethod is lower than the positive test method. The higher of the residual stress, the closer of the measurement result to the positive test method. When the residual stress is high (＞1 GPa), the results measured by negative test method can reflect true level of the residual stress. However, when the residual stress is low (＜1 GPa), measurement accuracy of the negative test method is usually decreased.