Explosion overpressure is an important indicator to describe blast load.And the results obtained by different methods have high discreteness.Based on this, the reflection coefficient formula of the relationship between incident overpressure and reflection overpressure is determined firstly by analyzing the experimental data chart fitting.Then a large number of theoretical calculation formulas and explosion test data were collected and transformed to analyze the distribution characteristics of explosion overpressure at different proportional distances.The results show that the probability density of explosion overpressure obeys exponential distribution when the scaled distance less than 0.5 m/kg^1/3.And obeys normal distribution when the scaled distance greater than 0.5 m/kg^1/3.The variation coefficient reaches the maximum value 1 when the scaled distance less than 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.According to the expected data of explosion overpressure distribution at different proportional distances, the calculation formula of explosion overpressure and the calculation formula of explosion overpressure distribution range with 95% guarantee rate are obtained by fitting.