Site monitoring is carried out on longitudinal stress of segment of a smalldiameter sewage shield tunnel of Huaifang Recycled Water Factory in Beijing. Five longitudinal stress meters are embedded in monitoring Crosssections 1 and 2 respectively (ring 976 and 1 054); the monitoring data are collected right after stress meter installation and are stopped when boring to ring 1 129. The study results show that: 1) The longitudinal stress of segment after 50 rings behind shield tail is 5% less than that when segment assembling. 2) The longitudinal stress of segment decreases with the distance between segment and shield tail increase during shield tunneling. 3) The longitudinal stress of segment increases firstly and then decreases with the distance between segment and shield tail increase during segment assembling. 4) The longitudinal stress of the segment goes stable around 0.20.3 MPa after the distance between shield tail and the segment is 108 rings. 5) With shield tunneling, the longitudinal stress of segment goes through four variation phases, i.e. periodical sharp fluctuation phase, dynamic stability phase, gradually decay phase and stable phase.