During shield boring, it is difficult to control the volume of foams injected and the quantities of different compositions of foams. The electrical control scheme of the foam system of shield machines is described, with CREC036 shield machine as an example. On CREC036 shield machine, the foam control system is consisted of PLC and PC. The quantities of different compositions of foams are accurately adjusted by means of transducer and electrical regulator. The test of the mentioned system in the plant and field demonstrates that good effects can be achieved. 