In order to solve the great difficulties and problems such as low efficiency and low accuracy in measuring the groove of crankshaft in automotive engine, a new method of crankshaft groove measurement based on shadow castingtechnology was proposed. The characteristic geometric size including radius, width and depth of crankshaft groove could be measured automatically, rapidly and precisely with this method. The measuring principle and process were introduced, and the key image processing algorithms and data processing methods including region of interest extraction, subpixel-precise edge extraction, segmentation and fitting of geometric primitives, characteristic size extraction, etc. were all presented in detail. This method has been verified by the crankshaft groove measuring system developed by us, and has achieved its engineering applications.