In order to meet the high requirement of oil sample testing environment and the control requirement of fast response and full automation, a control system with Siemens S7-1200 PLC as the control core was designed. The full automatic control of oil sample granularity detection process was realized by using granulometer, ABB dualarm robot, oscillator, stepper motor and other sensors. The work flow of the oil sample granularity detection control system was introduced in detail, and the control scheme of list scanning method was proposed. The application results show that the control system has stable performance, flexible process and multiple modes.