Abstract: Screen erosion damage is one common form of sand control failure in oil wells. Existing screen erosion model is too complicated to directly apply to the quantitative analysis on the screen failure risk of in-service oil wells. A mathematical model for the erosion mass loss rate was firstly established based on the fitting of a great number of laboratory experiment data. Based on the actual production situations of the oil field, the model was simplified further, the parameter C for characterizing screen erosion degree was proposed, and a mathematical model for analyzing the screen failure based on the dynamic production data of oil well was established. Then, the screen failure of sand-production oil well was calculated and analyzed with Bohai Q Oilfield as an example. The analysis result is completely in accordance with the field test result, indicating that this model can provide effective judgment on the working states of downhole screens in sand-production oil wells. Finally, the sand production risk prewarning method for in-service wells based on screen erosion was developed by analyzing and comparing the C value of in-service well and the critical value of erosion C_a, so as to realize the precise control of sand production risk in the oilfield.