To characterize the fragmentation degree of propellant charge quantitatively, the concepts of dynamic vivacity ratio and initial dynamic vivacity ratio （IDVR） were introduced. The dynamic vivacity ratio, which is the ratio of burning surface area of fragmented propellant charge to the corresponding not-fragmented propellants charges, and IDVR, which is the ratio of burning surface area of fragmented propellant charge to the corresponding not-fragmented propellants charges at the initial time were de- duced using the gas state equations of the closed bomb. The close bomb tests were done with three kinds of petal propellants with 19 holes and different lengths of 13.6 ram, 10 mm and 5 mm. The p-t curves of the propellants with different lengths were ob- tained. The IDVR of the corresponding propellants was gained by processing the p-t curves. The initial surface area of propellants with different lengths was obtained via calculation based on the geometrical shape, and then the iDVRs of the propellants were ob- tained. Results show that the IDVRs＇ results of tests are close to the calculated values, showing that the IDVR of the propellant can denote the fragmentation degree of fragmented propellant charge quantitatively.