Explosion overpressure is an important indicator to describe blast loading. And it has high dispersion for the overpressure results calculated from different methods. Based on this, the reflection coefficient of the relationship between incident overpressure and reflection overpressure is determained firstly by analyzing the experimental data chart. Then a large number of theoretical and test explosion overpressure data is gained by collecting and transforming the published results. The distribution characteristics under different scaled distance are studied. The results show that the probability density of explosion overpressure obeys exponential distribution when the scaled distance between 0.1 m?kg^(1/3) and 0.5 m?kg^(1/3) . And the probability density obeys normal distribution when the scaled greater than 0.5( m)?kg^(1/3) . The variation coefficient reaches the maximum value 1 when the scaled distance between 0.1( m)?kg^(1/3) and 0.5( m)?kg^(1/3) . While variation coefficient is in the range of 0.13 to 0.2 when the scaled distance within the range of 1.5( m)?kg^(1/3) to 6( m)?kg^(1/3) . The variation coefficient of reflect overpressure is a little bigger than that of incident overpressure. At last, based on the overpressure expectation of different scaled distance, the calculation formula of overpressure and distribution range under 95% guaranteed rate is gained by data fitting.