Aiming at the situation that the oil canvas needs to be disassembled when detecting the surface topography of the deformed oil painting in the traditional method, a method for nondestructive detection of the three-dimensional topography of the oil painting surface is proposed. The absolute phase distribution of the oil painting surface is obtained by the three-dimensional detection technology of structured light, the least squares method is used to fit the quadratic surface as the reference surface, and the difference between the absolute phase and the reference surface is used as the actual phase to obtain the height distribution of the oil painting surface. The test results show that the method can realize non-destructive testing without dismantling the oil painting canvas. It has an ideal detection effect for oil paintings with different degrees of deformation.