Abstract: Objective: To provide a simple and useful method of verifying the accuracy position of the radiation fields for three dimensional conformal radiotherapy plan.Methods: A simulator was used to take the radiography of 204 cases of conformal fields planned by 3DCRT;the conformal field radiography was transported to LANTIS system and compared with the planning-built fields;their coincidence and causes of error were observed and analyzed.Results: For the tumors on head and neck,the conformal field coincided well with the planning-built fields,and the errors in XY position was within 5 mm,but for tumors in chest and abdomen,the biggest error of field position was 12 mm.Conclusions: The method has the advantages of easy operation,low cost and practicability,adapting to the sections in middle-class hospitals using 3DCRT plan.The simulator verification can observe the tumor target and its nearby organs in risk at the same time.