The theoretical basis of coherent field imaging technique (also called the Fourier telescopy) is reconsidered. The limitations of the technique principle are analyzed by defining the measured object and deriving rigorously mathematical expressions. The reconstructed image of the technique ineluctably contains the gradient information about the object; as a result the technique cannot acquire the reflectivity of the object exactly. The computer simulation verifies the conclusion. Based on the conclusion, the reconstructed image of the technique can be evaluated and three-dimensional coherent field imaging technique may be developed.