Abstract: In order to analyze the causes for damage of casing head during drilling and well completion, understand the stress state and dangerous part of casing head during its service and determine its safety, simulation calculation and safety analysis were conducted to the casing head under multiple working conditions. The casing head calculation and calibration rules were established based on API standards and industrial specifications. In line with the actual working process of casing head on site, six typical working conditions like pressure testing and drilling were analyzed. The stress states of casing head under six working conditions were analyzed, the casing head deformation and stress distribution state were obtained and the dangerous part of the casing head was determined. Proper suggestions were made to the working conditions which did not conform to the calibration rules. The result of simulation calculation and analysis were consistent with the shape of casing head damage and so provided reference to safe and reliable casing head operation onsite.