本文提出了一种新的相衬显微镜的光路系统，这种系统非常适用于将普通显微镜改装成相衬显微镜．首先，叙述了相衬法的基本原理；接着提出了一种将相衬板置于物镜前方的相衬显微镜系统，并运用傅里叶光学证明了在非柯勒照明条件下在物镜前方确实存在物体的频谱面．这种相衬显微镜系统对于将普通显微镜改装成相衬显微镜来说，不仅简单实用，而且杂散光小，有利于提高灵敏度 In this paper, a new optical system of phase contrast microscope is proposed, which is very suitable for retrofitting ordinary microscope into phase contrast microscope. First of all, the basic principle of the phase contrast method is described. Then, a phase contrast microscope system with the phase plate placed in front of the objective lens is proposed. Fourier optics is used to prove that it exists in front of the objective lens under non-Koehler illumination Spectrum of the object. This phase contrast microscope system for ordinary microscope converted to phase contrast microscope, not only simple and practical, and the stray light is small, help to improve the sensitivity