As assembly and transmission parts, roll flat surface size and form position error are requested strictly. A method about measuring roll flat face symmetry was presented using sine gauge with dial indicator.This method is simple and practical. Using the method, the effections of joint knife and the concave heart part can be eliminated, and influence of the flat shape error on form-position error can be avoided, the measurement accuracy is improved, the actual machining precision of flat face symmetry is reacted more really. It has better guidance to actual processing.