The invention discloses a single-order air compressor. The single-order air compressor comprises a mounting bracket, a motor, a piston and a compression cylinder body; an air way of an exhaust port of the compression cylinder body is provided with an adjustable exhaust valve; the adjustable exhaust valve includes an exhaust valve cover, a spring, an exhaust piston and a valve cover module; an exhaust plug is fixed at the end part of the exhaust piston, and is blocked in a pressure relief hole; at least three bosses are arranged on the outer end surface of the valve cover module; all the bosses are uniformly distributed on a circle with the point of the axle of the valve cover module as circle center, and are equal in projection heights; at least three sets of steps are correspondingly arranged on the inner end surface of the exhaust valve cover; each set of steps at least includes two-stage step surfaces; the same-stage step surfaces in each set of steps are corresponding to the bosses on the valve cover module in position one to one; and two ends of the spring are respectively butted against the exhaust piston and the inner end surface of the valve cover module. The single-order air compressor has the beneficial effects of simple structure and capability of preferably adapting to different conduction trigger pressure requirements.