为了深入认识利用差分像运动法测量大气相干长度的特性，对差分像运动监测仪(DIMM)进行了深入的研究。基于理论分析和数值计算，讨论了DIMM中的几个重要问题，并阐明了解决方法，主要包括计算公式、子瞳大小及间距，从而提高了DIMM的测量精度，降低了DIMM的结构要求，扩展了DIMM的适用范围。

In order to have a thorough knowledge of characteristics of atmospheric coherence length measured by using differential image motion method, differential image motion monitor (DIMM) is studied deeply. Based on theoretical analyses and numerical simulation, several important problems existing in DIMM are discussed, and their solutions are elucidated. Problems include formulas, sub-pupil diameter and displacement of sub-pupils. Accuracy of DIMM is improved, requirements of instrument structure condition are reduced, and suitable scope of DIMM is expanded.