In a class of SIS epidemic model with birth and death, this paper considers the impact of nonlinear incidence rate on threshold value, improves the model, and mainly analyzes the influence of nonlinear rate on the epidemic threshold value based on considering the situation of the birth and death in complex network. Results show that nonlinear infectivity has severe effect on epidemic threshold value and that there is very close relation between epidemic threshold value λc and the death rate β with disease.