There is great significance in measuring objects on-line. Usually the contact measurement is used for measuring objects. 3D coordinate measurer and laser measurer are accurate ways to measure objects. But only points are measured by these ways. And many parts are shadowed by other parts or can not be contacted by probe, and are difficult to measure. It is not possible to measure objects on-line. Digital image processing is a fast developing subject. On the basis of these images the date result of objects are calculated by that system on aerophotographic way. We developed a system for that. With that system we got the date results of turbine blades. The accuracy of two results, one gets from our system to another from 3D coordinate measurer, are compared and analyzed in this paper.