Laser cutting error has large influence on the beam width of intravascular stents. Minor random variation in beam width of stents may significantly impact the expansion uniformity. In this paper, the relevant factors that may affect the beam width during the manufacture are investigated. Based on the randomization model, the pattern how the factors affect expansion uniformity is explored, and the method for calculating uniformity index is proposed. A detailed computation is made on the width randomization for the two expansion elements. The results show that with the increase of the value range of beam width, probability of uniformity index decreases gradually; the strengthening factor has large effect on the expansion uniformity. The method is meaningful for studying how the processing error affects expansion uniformity.