Beam position monitor(BPM) is used to measure the horizontal and vertical positions of the beam in the vacuum pip.　Before online installation,　it usually needs to be calibration.　High Intensity Heavy-ion Accelerator Facility(HIAF) and China initiative Accelerator Driven System(CiADS) will need a large number of BPM,　so it is a great challenge for BPM calibration work. In order to complete this work efficiently and accurately,　this research designs and develops an automatic BPM calibration system. The hardware of this BPM calibration system consists of 4 major sections,　they are calibration platform equipment, precise motion control device,　signal processing electronics and industrial computer. The control software was programmed by C to realize automatic calibration functions based on EPICS. A high-order fitting algorithm programmed by python used to solve the problem of smaller linear range of the capacitive BPM. It significantly improves the accuracy of position measurement after calibration.

Beam Position Monitors (BPM) are the non-destructive monitors used most frequently at nearly all linacs, cyclotrons, and synchrotrons. The most basic function of BPM is to provide the accurate position of the centre of mass of the beam for closed orbit feedback and other demands. However, due to the error of actual processing, the k value and the actual electric center will be different with the ideal k value and electric center of BPM, which requires us to accurately measure the k value and offset value of each set of BPM offline. There are 72 sets of BPMs in HIAF BRing & SRing, with 10 specifications and plate radius ranging from 180mm to 330mm, but the shape and size of the front and back pipes connected to bpms are variety during actual installation. Based on theoretical analysis, the k value and offset value of the BPM which electrode plates are too close to the flange are greatly affected by the pipes connected to bpm at both ends, and the measurement error can even reach 9mm. Therefore, this paper takes HIAF BRing and SRing BPM calibration as examples to explain how to accurately calibrate BPM.