In this paper, automatic test system of surface flatness was designed according to the characteristics of the no-till field by combining the PLC (Programmable Logic Controller), laser sensor and stepping motor automatic control technologies. Monitor and Control Generated System (MCGS) configuration software was used to form the interaction interface. Real-time data report and the trend line could be created by accessing PC machine to this system, and then the surface roughness detection was realized automatically. Compared with the traditional test methods, results of the automatic test system showed that the measured value is accordance with the artificial measured value, and the correlation coefficient between them was above 0.95; and the detection efficiency had been improved by 2.3 times. These results proved the effectiveness of the automatic test system in detecting the surface flatness of the no-till field.