Abstract: A new-style 5BY-5 type seed coater was developed in order to improve seed coating quality and meet the needs for seed usage during modern agricultural production. The automatic controlling system for the coater was successfully designed. PLC(Programmable Logic Controller) was taken as the control core of the system, and LCD touch screen was employed for human-computer interaction interface. The system integrated kinds of techniques including programming, frequency conversion, liquid flux monitoring and sensors, etc. The primary structure, working principle of the coater, selection of controlling system hardware and measures for anti-jamming were also introduced. Human-computer interaction software was programmed by the software of ProTool/Pro CS. System controlling software was programmed in the form of ladder diagram by Step 7-Micro/WIN, realizing kinds of functions including self-protection for working sections, accurate quantification, automatic controlling and humanized operation. Test results on wheat seeds coating showed that coating acceptability reached 99.2%, coefficient of variation on coating uniformity was 0.6%, which proved that the seed coater could improve coating quality effectively.