The influence of relativistic and thermal effects on plasma wave breaking has been studied by solving the coupled Vlasov-Poission equations. When the relativistic effect is not considered, the wave breaking will not occur, provided the initial perturbation is less than certain value as predicted previously, and the largest amplitude of the plasma wave will decrease with the increase of the initial temperature. When the relativistic effect is considered, wave breaking always occurs during the time evolution, irrespective of the initial perturbation amplitude. Yet the smaller the initial perturbation amplitude is, the longer is the time for wave breaking to occur. With large initial perturbations, wave breaking can always occur with and without the relativistic effect. However, the results are significantly different in the two cases. The thermal effects of electrons decrease the threshold value of initial amplitude for wave breaking and large phase velocity makes the nonlinear phenomenon occur more easily.