The invention relates to a snap ring type flanging connecting device for foundation pit assembly type internal bracings and belongs to the technical field of foundation pit internal bracing type supports. The device is located at the connecting portion between two foundation pit internal bracing components and is a steel structure assembly composed of two groove flanges, two snap ring type clamping plates and fasteners; one surface of one groove flange is fixed to the end of the corresponding bracing component, the other surface of the groove flange is closely attached to the surface of the other groove flange in an abutting mode, the two groove flanges are buckled through the snap ring type clamping plates, the two snap ring type clamping plates are locked through the fasteners to prevent the snap ring type clamping plates from getting loose outwards and falling off, and therefore the device forms a stable whole. According to the device, there is no need or a little need for bolt fastening operation, the splicing speed of a foundation pit assembly type internal bracing structure is increased, and foundation pit deformation caused by insufficient supports during erection of the internal bracings is reduced; the bending moment at the connecting point acts on the groove flanges and the snap ring type clamping plates to generate shear force, the shear surface is continuous and large in area without stress concentration, and the structure is reasonable and reliable.