Abstract: Drilling risk control is the key for promoting drilling efficiency,construction safety,cost-saving and profit.Some real-time drilling monitoring and alarm systems have been developed in recent years in China.Most of these systems lack functions related to potential risk prediction function before drilling and risk tracking and assessment after drilling.A model for quantitative evaluating the probability and severity of drilling risk was developed on the basis of causes of drilling risks.In addition,a visualization representation method was set up as well.And together,a real-time diagnosis method was developed based on drilling risk symptoms,and a drilling risk case knowledge database was also established as an auxiliary resource for risk prediction.Historical data of 5 existing wells were used for simulation and optimization of the model.The optimized model was used in over 10 wells.With completed and accurate geologic data available,the discovery rate of common risk reached 86%.The model was demonstrated to have important performances in control over high-level risks.The innovative drilling risk assessment system could provide necessary technical supports for sustainable optimization of drilling program and eventually achieve objectives in "risk-free" drilling operations.