Abstract: A comparative study on water content accuracies measured by two neutron probes which are IAG-Ⅱ（made in China）and 503DR（made in U.S.A.）were conducted.The results show that the average accuracy of IAG-Ⅱ against soil drill is a little higher than that of 503DR; the stabilities of IAG-Ⅱ in the condition of 14 and 25 are better than those of 503DR；the stability of 503DR in the condition of 52 is better than that of IAG-Ⅱ and the effect of temperature on 503DR is less than that on IAG-Ⅱ.The two neutron probes can be applied in professional work and study.Using statistical method，two regression equations built in 1991 and 2002 for 503DR are compared.The results show that the residual standard deviation of two regression equations do not have a notable difference and between the constants（a）and coefficients（b）of two regression equations，there exists a notable difference，so the two regression equations can not be merged.