Abstract: The site coefficient is a key index for considering the seismic site effects in various national and regional standards, which determines the criterion of earthquake-resistant design, but there exist significant differences between domestic and foreign standards. Based on the ideal soil-bedrock site model, an analytical expression for the quantitative relationship between soil site and reference bedrock is derived and examined through numerical simulation. The general rules of site amplification coefficient are put forward, and the reliability of different recommended values are verified. The results indicate that the soil ground motion is always amplified in the whole frequency domain compared to the reference bedrock. The site amplification coefficients show the overall increasing trend with the softening of the site, and are consistent with the suggested values in the new NEHRP provisions of the United States of America. The coefficient of soft site in China is seriously conservative and the value is less than 1.0 under strong vibration, which is clearly unreasonable. It is debatable whether the site coefficient of class site IV should be generally less than that of class site III in China's code.