Abstract: Objective To establish a monitoring and early warning system for symptoms of major infectious diseases in Changning District,Shanghai. A method was explored to collect data, establish threshold and identify abnormal signal for major infectious diseases.Methods Hospitals and schools were selected as monitoring points, in which undefined pneumonia, influenza, bacterium diarrhea, cholera, infectious diarrhea, measles, chickenpox， hand-foot-mouth disease and type-B encephalitis were monitored as target diseases and related surveillance on the symptoms of these diseases were carried out. Early-warning threshold of each symptom groups was calculated by the mobile percentile method.Results The monitoring and early warning system for symptoms of major infectious diseases has been designed and developed,which has many functions such as syndrome information collection, data import, early-warning parameters, daily warning value, abnormal automatic report and warning to abnormal message, early warning data query, user management and rights management.Conclusion Through this research, a software which could collect electronic data, automatically analyze and make early warnings was developed. A set of method and mechanism was formed for data collection on symptoms,threshold establishment，abnormal signal identification. The information system for symptoms of major infectious diseases can be used by disease prevention and control agencies to carry out symptom monitoring, which has positive significance in the improvement of early warning and detection for outbreak seedling of infectious diseases.