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Herein, we investigated the performance of a Si waveguide-integrated superconducting nanowire single-photon detector (SNSPD) with an arrayed waveguide grating (AWG) comprising SiN/SiON. The system detection efficiency of SNSPD with AWG was unchanged whether the AWG is at a room or cryogenic temperature because the insertion loss was unchanged while the passband shifts 1.7-nm lower at cryogenic temperature. On the other hand, the dark count rate of the SNSPD with AWG decreased by approximately 20 dB when the AWG was at cryogenic temperature. The AWG at the cryogenic temperature functioned as a cold optical bandpass filter, which suppressed the dark count rate due to the background room-temperature blackbody radiation through fiber optics. The noise equivalent power (NEP) of the SNSPD with AWG improved from 4.8 × 10-17 W/Hz-1/2 for the room-temperature AWG to 2.2 × 10-18 W/Hz-1/2 for the cryogenic-temperature AWG. Results demonstrated that the integration of photonic circuits with SNSPD at the cryogenic temperature benefited not only scalability but also performance.