Abstract: The essentiality of determination on optimum deposited area of substrate support has been analysed. Using a experimental method, the arch sustrate support of ZZ-SX500 model optical plating machine hasbeen studied. Theoretical foundation and practical results of the experimental method have been given. The reliability evaluateing test on the key experimental instrument namely MKG-5 photoelectricity extremum model film thickness measuring-controling instrument has been conducted.