This paper explores the methods for studying regional economic difference in the aspects of research unit's being decided, measurement index's being chosen, and measurement means' being selected. It also points out the advantages and disadvantages of each method by taking 31 provinces, autonomous regions, and municipalities in mainland China as regional study unit,and per capita GDP as total index to measure regional economic difference.It quantitatively measures the overall leveland the characteristics of dynamic variation of the recent inter-provincialeconomic difference from the angles of standard deviation , and standard deviation coefficientof every region's per capita GDP.The absolute difference rose linearly and the relative difference wavelike. The frequencies distribution of every region's per capita GDP is a kind of positively slanting distribution, deviating normal distribution greatly. Every year, only a few provinces' per capita GDP is above the average level of the whole country. It also quantitatively measures the characteristics of spatial structure of this differential variation from the angles of the ratio of every region to the whole nation, and the difference of every region's relative development rate. Coastal areas are developing faster, in contrast with the inland areas, especially some western regions. There is a narrowing tendency in economic difference among coastal provinces, but in contrast there is a widening tendency among the east, the middle and the west. The spatial structure of the three belts was strengthened in the 1990s. The regression model between the growth rate of whole nation's GDP and the standard deviation of every region's per capita GDP was set up and according to this model the warn standard of inter-provincial economic difference was probed in this paper. Theoretically, the standard deviation of per capita GDP in 1994 had already broken warn standard. Moderately balancing policies should be carried out right then, so as to control the widening difference and to make each region develop harmoniously.