Abstract: With the establishment of heavy ion cooling storage ring(CSR) in Institute of Modern Physics, Chinese Academy of Sciences, the DPET(double-sector positron emission tomography) detector is developed. The structure of DPET detector, the principle of detection and characteristic of design are particularly discussed, including the structure of detection crystals, the optical fibers, the design of the signal readout circuit and the electronics data acquisition system. Some results of detector unit performance test are also presented.