Shield is a key equipment for tunnel construction. The thrust system of a shield directly affects the attitude, boring alignment accuracy and advance rate of the shield. When some shield is boring in soft ground, it is difficult to control the attitude of the shield and pitch may occur. In the paper, the reasons for the above mentioned phenomenon are analyzed on basis of the control modes of the thrust systems of the shields supplied by different manufacturers. Pressureflow compound control mode and proportional pressure reducing valve control mode are two major control modes of hydraulic system of shields. The dynamic response of the actuating mechanism of shields under the two mentioned control modes are compared by means of AMESim simulation, theoretical analysis and monitoring data analysis, so that the characteristics of the operability and attitude control of shields can be analyzed and compared. The paper can provide reference for the design of the hydraulic thrust system of shields, as well as for the type selection and operation of shields. 