Receiving the investigation letter from the tax bureau means that the parties need to assist the tax inspection department of the tax bureau to carry out tax inspection, and provide the tax inspection department with the source of the case and fast, accurate and convenient tools and means to investigate the case. The case selection department uses computer analysis, manual analysis, man-machine combination analysis and other methods to screen the case source information. If it is found that there is a suspicion of tax violation, it shall be determined as the object of investigation.