Some problems, i.e. nontargeted gasliquid ratios selection and serious foam waste, exist in compressed air foam system of EPB shield. Hence, a complex foam generator is designed based on nettype and media fillingtype foam generator; a compressed air foam system is developed, and its foaming performance is studied. The main factors, including air flow, liquid flow and air pressure, affecting the performance of foam generator are determined by experiments of the foam flow, foaming ratio and halflife of foam. It is proved that the foaming performance of the compressed air foam system can reach the best when the gas pressure reaches 0.3 MPa, gas flow rate reaches 230 L?min-1 and gas liquid ratio reaches 50. The foam is used in the red clay conditioning test, and the testing results indicate that the red caly can be in plastic and flowing state when water content rate is 26%-29%, foam amount is 10%-45% and gasliquid ratio is 40-75.