VDI2614/2634 is a kind of common method of precision evaluation for 3D optical measuring systems.In order to formulate a national standard named Measurement Specification of Optical 3D Geometry for Forgings & Stampings and Its Dies，a new evaluation method for optical measuring system imposed on forgings/stampings is proposed and the testing project is also drafted.With the evaluation, each group measuring value is considered as a single subsystem, and the minmax-difference， mean difference and the mean square value of each group are calculated. Then,the ratio of the mean difference to the measurement mean value is defined as the system-relatively error of subsystem and the ratio of the minmax difference to the measurement mean value is defined as the accidence-relatively error of the subsystem.In consideration of the relatively error and weights completely, the system errors and accident errors of the measurement system are calculated. For the reunification of evaluation standard, the concept and the calculation method comprised of standardized system precision, standard accidental precision and standardized precision are put forward. The XJTUOM optical measuring system developed by ourselves has been evaluated by the proposed approach, then the standard precision of 0.89 is obtained,which provides a reference for formulating national standards.