A sewer pipe inflow and infiltration diagnosis method based on a distributed fiber-optic temperature measurement system is provided. The inflow and infiltration diagnosis method includes the following steps: S1: transmitting, by an optical time-domain reflectometer, an original optical signal to a temperature sensing fiber-optic cable provided in a sewer pipe; S2: feeding back, by the temperature sensing fiber-optic cable, a modulated optical signal to the optical time-domain reflectometer due to a temperature effect; S3: subjecting the modulated optical signal to photoelectric conversion, so as to acquire binary information; S4: converting the binary information into decimal information; S5: drawing a spatiotemporal map of a water temperature; and S6: eliminating a background noise value, identifying an abnormal water temperature point, determining an inflow and infiltration point of the sewer pipe, and determining an abnormal inflow and infiltration point of the sewer pipe.