Conventional simulation tools that verify the layout of a subwavelength IC against the silicon it is intended to produce. It reads in the layout and simulates lithographic process effects, including optical, resist and etch effects. Then compares the results -- the simulated "silicon image" -- with the original (intended) layout, reporting out-of-tolerance regions. We here introduce a reverse engineering method that use ready database to simulate unknown pattern. By using this method, you can get more fast and accurate results then conventional simulation tools. We will discuss the advantage and disadvantage of this method and its application.