【摘要】Irregular economy develops very rapidly in world economy these years and it is also one of the most difficult problems in economy to research and estimate.There are several methods to estimate the scale of irregular economy.The author defines the range of irregular economy and interprets the characteristics of irregular economy and tells us the connection with the National Accounting System.Secondly,according to the characteristics of Chinese currency flow,the author revises the method of currency ratio and makes empirical analysis and receives a good result.