【Objective】 To observe the incidence of secondary lactose intolerance (SLI) of diarrhea children, observing the efficacy of treatment after giving medical lactase import agents and lactose-free milk powder intervention. 【Method】 To detect the urine of diarrhea children by the urinary galactose kit, children with positive results were randomly assigned to three groups, lactose-free milk group, without lactose-free milk group and control group, to compare the curative effect and course of the three groups. 【Results】 The incidence of diarrhea secondary lactose intolerance (SLI) was related with age, the younger ones had the higher incidence; various age groups were significantly different(P＜0.01); SLI was infection-related, and rotavirus infection group was higher than other groups(P＜0.005); there were differences of the total effective rate to three treatment groups(P＜0.005), and there was no difference between the first two groups; the course of the third group was different(P＜0.01), and there was no difference between the first two groups. 【Conclusions】 The younger ones have higher incidence of SLI.The incidence of rotavirus infection is higher than other causes of morbidity; imported medical lactase and lactose-free milk powder formulations may enhance the effectiveness of treatment to shorten the course of disease,but to supply lactase is the fundamental method to solve the question of SLI.