Abstract: This paper deals with the quality of statistical data in terms of error. It holds that the quality of statistical data is a matter of error in nature. In view of total error, however, the system error is much more difficult to treat than the random error is. The writer makes a detailed analysis of the characteristics structures and reforms of the system error, and points out that what is the most important is not measuring the value of the system error, but discovering the data with the system error and removing its effect.