The invention discloses a system and a method for controlling front soil pressure balance of a quasi-rectangular shield. The system comprises: a soil pressure monitoring device, comprising a monitoring host in communication connection with a screw conveyor, and multiple pairs of soil pressure sensors which are in communication connection with the monitoring host and are symmetrically distributed on both sides of a top part, a middle part and a bottom part of a soil cabin of a quasi-rectangular shield machine; a soil pressure compensation device, comprising thrust cylinders arranged on both sides of the soil cabin, wherein the thrust cylinders are in communication connection with the monitoring host; a soil improvement device, comprising a plurality of improvement regions symmetrically distributed in the soil cabin and grouting equipment for respectively grouting the plurality of improvement regions, wherein the grouting equipment is in communication connection with the monitoring host. According to the invention, a soil pressure value of the soil cabin of the quasi-rectangular shield machine is monitored in real time through the soil pressure monitoring device; the front soil pressure balance of the quasi-rectangular shield in a tunneling process is collaboratively controlled by utilizing the soil pressure compensation device and the soil improvement device and cooperating with the control of a rotation speed of the screw conveyor.