Causes to leading to bias and common bias in clinical researches of surgery LIU Xu-bao.Department of General Surgery, Huaxi Hospital, Sichuan University,Chengdu610041,China Abstract Bias is leading causes to decrease reliability of surgical research. Philosophy of Surgical doctors and clinical character of surgery may be correlated with defect in research design, which is cause of bias. So to avoid bias in research, a series of interventions should be applied, such as to select relatively strict target objectives, to use scientific proposal of design, to adopt reasonable control, and to apply blind observation and objective detections. Conclusion: bias is important factor to decrease research quality of surgery. Only way to abate or avoid bias is use scientific proposal of design in researches.