One of the main reasons affecting visual acuity after cataract extraction and intraocular lens implantation is postoperative astigmatism. The postoperative astigmatism is the vectorial sum of preoperative and surgically induced astigmatism. The surgically induced astigmatism is a vector which includes size and direction. And the analysis of surgically induced astigmatism is the necessary step before cataract and refractive surgery. This paper has summarized the method of calculation of surgically induced astigmatism.