A photon conversion finder （PCF） based on track information from the main drift chamber （MDC） of the Beijing Spectrometer （BESⅢ） at the Beijing Electron Positron Collider （BEPCⅡ） is developed. The validation of the PCF is done by reconstructing π 0 and measuring the branching fraction of J/ψ→γη . Using the developed PCF tool, we mapped the materials from the interaction point through the BEPCII beam pipe up to the inner wall of the MDC.
