The utility model relates to a diagonal collision sensor for a car which is used for a car air bag. A bolt is fixed at the center of the top of a cover. The part of the bolt inserting into the outer cover is sleeved with a bracket which is provided with a micrometric regulating screw. The bracket is sequentially connected with a petal disk type elastic element, a suspended ball and a suspended pendulum. The micrometric regulating screw is pushed on the petal disk type elastic element. The center of the bottom of the suspended pendulum is provided with an electric brush. A round contactor is arranged at the outside of the electric brush, and the round contactor is connected with a lead which is connected with and extents out of the cover through a wire feeding coil positioned on the cover. An insulation seat and a soleplate are arranged on the bottom of the cover. The utility model solves the technical problem that the existing collision sensor of the air bag is not suitable to any diagonal collision, and can respond effectively and synchronously when any diagonal collision occurs at a preset speed so as to input the starting signal without hysteresis. The utility model has the advantages of rational structure, small volume, low cost, good economic benefit, reliable performance, mass production and stable quality.