An circuit board assembly includes a first circuit board, a second circuit board stacked with the first circuit board, and a connection plate connected between the first circuit board and the second circuit board. The connection plate includes a signal transmission part and at least one ground part at a spacing to the signal transmission part. The ground part can be used as a reference ground for a signal transmitted by the signal transmission part, so that the characteristic impedance of the signal transmission part is controllable, and the signal transmitted by the signal transmission part has strong continuity, thereby maintaining good matching performance and reducing an insertion loss caused by characteristic impedance mismatch.