This paper proposes a stress analysis model for the cracked PVC pipe. The cracked PVC pipe is rehabilitated with an inner composite epoxy material by a dig-free method. The optimal thickness which can get the maximal flow rate after rehabilitated will be found by the finite element model. When the crack width of the pipe with 324 degree crack angle is 30 mm, the optimal thicknesses will be obtained with the compression ratio of 5%. The optimal thicknesses of the phi 300, phi 400, phi 500 and phi 600 PVC pipes are 0.6, 0.8, 1.1 and 2.5 mm respectively. With these optimal thicknesses, the flow rates of rehabilitated pipes are lager than 98% the flow rates of original pipes.