The Collins formula in spatial frequency domain is generalized into axially nonsymmetrical optical system in terms of tensor analysis method. Based on this formula, the tensor ABCD law in spatial frequency domain is derived. The Collins formula and tensor ABCD law in spatial frequency domain provide the relation between the input spatial Fourier spectrum and the output spectrum directly. They have advantages in treating the problems concerned with spatial Fourier spectrum, such as spatial frequency filtering, optical transfer function of imaging systems and the propagation of general astigmatic Gaussian beam in free space, and so on.