The study of crab-sepa standard pattern is for the following purposes: 1. Historical and evolutional study of crab-sepa from the reign of King Rama VI to contemporary period. 2. Study the standard pattern of crab-sepa according to Thai music methodology. 3. Study the significant factor that makes the crab-sepa property discrimination. It is found that sepa knowledge in the reign of King Rama VI was encultured and made refinement by the royal court through glorious status. The result had occured in the scholar appearance and oral tradition conserved along the Thai social context until now. The standard pattern of crab-sepa according to the Thai music methodology was settle down from the past, but the indefinite conclusion occured. The crab-sepa standard pattern is found to be consisted of 3 main properties: sonic standard pattern, performing standard pattern, and material standard pattern. There are 3 factors in crab-sepa property' discrimination: the ditch shaping, the specific grain, and the size of crab-sepa.