We study, using a finite-different method, single vortex structure of a s+id-wave superconductor by solving a time-dependent Ginzburg-Landau (TDGL) model for high-T c superconductors. We find that, below a phase transition temperature, the order parameters indicate twofold symmetry, whereas a fourfold symmetry appears beyond the temperature. We have also investigated the effects of thermal fluctuations on the pairing symmetry while existing an additive noise or a multiplicative noise in the TDGL models. The regular vortex pattern will be distorted and disordered steadily as the noise level increases. And, it becomes no longer recognizable as a sufficiently high magnitude of noise exists.