The cutter suction dredger uses a triangle broad fin anchor as the positioning anchor for sideway dredging. Aiming at the problem that the grasping force of the sideway anchor is limited under the soft soil，we carry out the force analysis of the sideway anchor by using the limit equilibrium principle of soil and establish the calculation method of the grasping force of the sideway anchor. Based on the calculation，the main factors affecting the grasping force of sideway anchor are the depth of anchor crown into the soil，the failure angle of soil wedge，and the angle of anchor rod. The results show that the deeper the anchor crown goes into the soil，the greater the anchor grasping force. The smaller the angle between the anchor rod and the horizontal plane，the greater the anchor grasping force. With the gradual increase of the failure angle of the soil wedge，the anchor grasping force first decreases and then increases. When the soil wedge failure angle is between 20° and 25°，the anchor grasping force is the smallest，and the anchor grasping force coefficient is about 14.