The splitunit rectangular pipe jacking with high precision and high efficiency is very difficult. Hence, study is made on the applicability of splitunit structure, design of position and attitude control, and design of excavation system of composite small cutterheads of rectangular pipe jacking machine boring in the underground parking lot project of CREG. Some conclusions are drawn as follows: (1) A new type of combination method is proposed, which solves the problems of structure adaptability of splitunit rectangular pipe jacking machine, such as sealing and pipeline communication brought by equipment combination. (2) The hinged structure of shield body is innovated; and the compound position and attitude control methods of the splitunit pipe jacking machine, i.e. coordination deviation rectifying by deviation cylinder and double screw convey mucking, and rotation deviation rectifying by multicutterhead speed and direction control and loading control along radial direction of main machine, are put forward. (3) The variation law of torque coefficient of small cutterhead with cutterhead diameter and layout is discussed by regression analysis method; and a calculation model of torque coefficient of small cutterhead, with diameter less than 3 m, is built, which can provide a theoretical basis for drive configuration of the multicutterhead system.