The nonlinear parametric vibration of main cable in suspension bridge was investigated. The local vibration of tower was considered the parametric excitation of main cable, the equation governing the parametric vibration of main cable was derived using Newton Law considering sag and geometric nonlinearity. Then the Galerkin and the multiple scales method were used to analyze the parametric vibration of main cable. A case study of main cable of a suspension bridge, the first 20 frequencies of the tower was calculated by means of the finite element program, through the frequency of tower and the first in-plane frequency of main cable matching, it was very possible that the 11th, 13th order vibration of No.0 tower and the 4th order vibration of No.3 tower excited the parameter vibration of main cable, the time history and the variation law of cable tension were examined. As a result, the main cable is prone to vibration parametric vibration when the local frequency of tower is about 2 times the frequency of main cable. The parametric vibration has a considerable effect on the displacement of main cable, and the increment of cable tension is small.