Abstract: The preparation and cyclodehydration of N-Substituted phenylmaleamic acids were studied. The raw material, N-Substituted phenylmaleamic acids, N-Substituted phenylmaleimides and their mixture have been characterized by nuclear magnetic resonance spectroscopy. From the appearance,decrease or change of COOH proton resonance (～10 ppm), HC=CH proton resonance peak, conversion characterization of maleamic acids and maleimides were determined. The chemical shifts related to draw electron of substituting group and coupling constant were investgerted.