Abstract: In PET (positron emission tomography) system, the single-rod source spends a lot of time on the photon-attenuated scan. Although the three-rod source can reduce the scanning time, it brings a lot of random coincidences. A restricted single-photon algorithm is therefore designed for randoms correction due to the three-rod photon-attenuated scan, i.e. to provide a random sinogram for each and every rod position so as to filter all by three fan-beam acceptance windows. Then, a practical random sinogram is provided comprising all filtered random coincidences. The algorithm was evaluated by the image quality and correction accuracy of attenuation as specified in NEMA standard. Experimental results showed that the proposed algorithm can obtain the same image quality and correction accuracy of attenuation just like what can be obtained from single-rod source with half of the photon-attenuated scanning time saved.