Abstract: Short-term statistical characteristics of moving sequences is discussed in this paper. To get reasonable results, real time motion image sequences are used, bit numbers of each macroblock after encoding using MPEG(Moving Pictures Experts Group) compression algrithom is analyzed.In the mean time, the effect of quantiser scale and quantiser matrix to the statistical property is also researched. Simulation result shows that quantiser scale plays a important role in the statistical property, while quantiser matrix has little influence. If small quantiser scale is adopted, image contents will affect the probability distribution at low bit end, and its influence decreases as the quantiser scale is relatively large.