Coin can be destroyed during the usage if there are some dirty, corrosion, deformity and abrasion areas on the coin surface which can impact the continuous usage of coin. Some key technologies for dirty area recognition are especially investigated in this paper. Firstly, the dirty area recognition and quantitative algorithm are developed according to the statistic results of different material coin. The algorithms which are based on fuzzy intent judgment algorithm can automatically calculate the disfigurement area. Secondly, in order to prove the effectiveness and robustness of the algorithm, repeated test of relevant algorithm is researched. The experiment results prove the validity and practicability of the related algorithms.