Longterm field test is made on the stress of the segments of Nanhu Road Tunnel in Changsha, the rule of the timedependent variation of the applied load and internal force is summarized, the distribution of the internal force in different construction stages is studied by means of beamspring model and comparison is made between the study result and the field test result. The research result shows that: 1) Eccentric load state is easily formed when the segments move out of the shield tail; 2) Grouting has great effect on the distribution of the internal force, which increases significantly because of the grouting; 3) With the monitoring going on, the internal force, especially the axial force, still has a small increase.