Physicists have been looking for ways to derive the bound state energies of different potentials. One of these methods is the quantization condition derived by WKB approximation, which easy to comprehend and imagine. However, there are still some defects in this theory. In this thesis, we’d checked the applicability of WKB under different conditions and tried to find out higher correction terms for quantization conditions. Besides, we'd calculated the bound state energies of some potentials that ”soft” turning point quantization condition isn’t applicable by starting from the meaning of quantization condition.