In present, there are two methods for controlling flow rate and pressure in the market. One is to adjust the main path and bypass through a proportional valve, and the other is to control the variable frequency pump through a frequency converter. The proportional valve adjustment is generally applied in the normal temperature section and high-temperature section. This method is suitable for cases where the required response time is long, the flow control accuracy is not high (around 0.3L/min). If high-precision control, short response time and low-temperature resistance are required, the general proportional valve spool can not meet the requirements. The cost of imported high-precision proportional valves is high, and they are prone to leakage at low temperatures. The adjustment method of controlling the variable frequency pump through a frequency converter avoids the defects of the proportional valve.