Objective To investigate the value of PCT in the diagnosis of severe infection in children.Methods The clinical data of patients with infectious diseases treated in our hospital from December 2013 to February 2016 were retrospectively analyzed.According to the degree of infection,the patients were divided into local infection group and severe infection group,At the same time,the clinical data of 50 children with non infectious diseases were selected as control group.The differences of serum PCT and cytokine levels were observed between the three groups,at the same time,according to the prognosis of patients with severe infection group were divided into improvement group and deterioration group,The differences of serum PCT and inflammatory cytokines levels in the patients with severe infection in the improvement group and the worsening group,Analysis of the correlation between PCT levels and serum inflammatory cytokines levels in children with severe.Results There were significant differences in the levels of PCT,IL-18,IL-6 and hs-CRP between the three groups,which were from high to low: severe infection group,local infection group and control group; Deterioration of PCT,IL-18,IL-6,hs-CRP and levels were higher than the improvement group(t=-10.099,-8.949,-10.827,-2.088,P<0.05); The level of PCT were positively correlated with IL-18,IL-6 and hs-CRP levels in children with severe infection(r=0.385,0.412,0.408,P=0.012,0.008,0.017).Conclusion PCT has a good diagnostic value in children with severe infection,and it is closely related with the level of inflammatory cytokines in children with severe infection.