Abstract: For non-interceptive position measurement of annular beams with travelling radius of 24mm, beam radius of 19mm, thickness of 3mm,the BPM technical scheme was chosen. The electric field on the wall of a circular chamber produced by an annular beam is compared with that of a pencil beam located at the same axes. It is proved that BPM system can be used for position measurement of annular beams. Taken a single-point non-uniform model, the influence of the azimuthally non-uniformity on measurement accuracy is analyzed. And it is revealed that 10% single-point non-uniformity caused a 0.1mm measurement deviation.