Disclosed herein is a collision detection system for a vehicle. The collision detection system for a vehicle according to the present invention includes a sensor unit and a control unit. The sensor unit measures impacts A and B along two axes that intersect each other in diagonal directions. The control unit calculates a longitudinal impact X and a transverse impact Y using the measured impacts A and B, and determines the direction of collision and whether to operate at least one device for protection against collision-related injury using the impacts.