Abstract: Optical module is widely used in optical communication,so how to supervise the working state of the optical module is very important.Digital diagnostic,which can provide an effective method to diagnose the performance,is attached importance by engineer.One part of digital diagnostic is ROSA power calibration,which includes internal calibration and external calibration.The paper introduces a new method of calibration which merges the internal and external calibration.The experiment proves that the method can improve the power solution in low power,and the result is accordant with SFF 8472. At last,we give the physical diagram of automatical calibration system and the software to calibrate automatically.