Electro-optic products sometimes require sapphire plate lenses of high quality that are highly accurate in terms of flatness and parallelism and are in a scratch-free condition. This is difficult to achieve by conventional methods (for example, with a general polishing machine, single-sided polishing machine, etc.). In addition, the preparation of the laps and the lapping process are inconvenient and time consuming. We have designed a new method for lapping sapphire flat lenses that is based on the mechanism of the correction of a double-sided lapping machine's lapping plate and the measurement of highly accurate parallelism by means of lateral shearing interference. This method can accurately and efficiently lap extremely hard sapphire flat lenses.