Abstract: The mapping and shimming of cyclotron's main magnetic field is an important direction of cyclotron technology research. In order to meet the theoretical requirements of the cyclotron’s main magnetic field shimming, the edge shimming method adopted requires high precision in the reprocessing of the main magnet shimming. However, due to the fact that the primary processing method of the insert is the form of matching, the material of the shimming block itself is low in hardness, thin and long in shape, and under the condition of strong magnetic field, the actual amount of shimming processing is very small, and slight disturbance will cause drastic changes in the magnetic field, so it is very important to ensure the precision of the re-processing of the insert to realize the function of the cyclotron. Based on the way of obtaining the theoretical edge curve, the machining accuracy mapping and the actual machining method of the edge curve are put forward, and considering the coordinate system relationship, a fixture is designed to ensure the machining accuracy of the shimming block, which can fix two shimming blocks at the same time and provide a suitable reference point to realize the position reproduction of the shimming block on the accelerator. The tool is applied to the shimming processing of 16 Mev cyclotron. The mechanical measurement error of each shimming result is 0.02 mm, and the accuracy of the actual processing magnetic field and the theoretical padding magnetic field is better than 10⁻³ after magnetic field retest.