Abstract: It is suggested that unified detecting regulations and calibrating method be drawn up to solve the problem as to standardizing the capacity of an inner-floating-roof tank. The author gives out the methods to standardize the capacity under the floating disc and that during rising of the disc. Here is allso presented in the article the formulas and workout direction concerning the measurement and calculation of liquid level difference, revision of static Pressure capacity, the work-out sequence of the capacity table, etc.