Generally speaking, there are no set rules that govern the sequence of numerous measuring assignments of the workpiece in measurement by CMN. In most cases, On site operators determine the order of the measuring points based on their experience. Thus, there is yet to be a set of effective empirical rules. In this article, the grid diagram method is proposed to conduct collision-free analysis on a workpiece plane with simple spherical convexity. The grid diagram method established has never been suggested in previous literature related to measurement, and is an original method in the study of collision-free planning for measurement. In this article, we proposed a grid diagram to describe the barriers in the measurement space. Then the distance configuration method and other rules are applied to establish the collision-free planning through. This article first, the positions of measuring points and measuring path on the workpiece plane are already known. Then grid diagram method is used to conduct collision-free analysis on the spherical convexity on the workpiece plane, which can generate interference, before the collsion-free path is obtained. Finally, a case study of a plane workpiece with spherical convexity is given in this article to explain the steps required to complete collision-free planning using the proposed grid diagram method.