The talbot self-imaging conditions of the plane periodical objects are presented. It is proved theoretically that restriction of the angle v, 2RaRb cos r=integer, is not a necessary condition. If the cross terms of the spatial frequencies for the unit cell of periodical object are much smaller than the main frequency terms, the restriction of the angle is not necessary. In this case, any two-dimensional periodical object can be self-imaged. The experimental results presented in this paper are in accordance with the theoretical analysis.