The invention discloses an indirect measuring apparatus for a vehicle operation status parameter and a calibration method. The operation status parameter includes a brake power. The apparatus includes: a chassis dynamometer, a fender pile, and a drawing force transducer. The calibration method includes the following steps: parking a vehicle on a rotary drum of the chassis dynamometer of the vehicle; connecting a hydraulic sensor to a wheel cylinder oil pipe; starting the vehicle and accelerating the vehicle to 70 km/h; treading a brake pedal to a half position; calculating an indirect measuring result of the vehicle operation status parameter on the basis of the chassis dynamometer of the vehicle and the drawing force transducer; comparing the indirect measuring result with the wheel cylinder oil pressure; and on the basis of a comparing result, calibrating the indirect measuring. According to the invention, the apparatus and the method are suitable to use the chassis dynamometer to conduct calibration on indirect measuring of the vehicle brake power and make an accurate indirect measuring result. The apparatus and the method guarantee measure parameters through the chassis dynamometer and solve the vehicle brake power, and at the same time guarantee similarity between indirect measuring precision and direct measuring precision, and greatly increase convenience and effectiveness in measuring the vehicle brake power.