Because of limited sample numbers, imprecise data and dynamic error, statistical method based on probability theory has some shortage in neutrons data processing. Based on Dempster-Shafer (D-S) theory, a method of statistics of neutrons data is described. Appling the basic assign, belief function and plausible function, the lower and upper probability for neutrons randomly distribute to some sets was presented, so was the average neutrons number. The new method of statistics is especially suitable for imprecise data and not restricted by sample numbers.