Wavefront curvature sensor has been applied in the fields of adaptive optics and optical metrology. It is assumed that the intensity of the incident wavefront is uniform in these fields, but this assumption is not in accord with the principle of the curvature sensing technology. The theory self-contradiction of the wavefront curvature sensing technology is analyzed qualitatively in this paper. By means of the diffraction theory and geometrical optics approximation, the signal expression of wavefront curvature sensing under nonuniform intensity is deduced, and the signal error is analyzed as well. The results show that nonuniform intensity introduces the dot product of intensity logarithm and wavefront gradient. Under most conditions, the dot product can be ignored, so the assumption of the uniform intensity is rational. But in the laser Gaussian beam whose intensity magnitude changes, error occurs.