The invention relates to a tester for testing the fuel economical efficiency of a light-weight automobile. Aiming at the problem that an automobile can be only tested on a simulation chassis rotary drum dynamometer because the existing fuel measurer can only measure transient fuel consumption or kilometer fuel consumption, so that the economical efficiency of an actual automobile cannot be tested on a road according to a rule, the invention provides a tester for testing the fuel economical efficiency of the light-weight automobile. The tester mainly comprises a fuel consumption meter, a singlechip, an interface chip, a control panel, a display, an automobile speed sensor, a main flow sensor, an auxiliary flow sensor, forwarding gear sensors, an analog / digital (A / D) converter, a circuit and the like. Fuel consumption can be tested according to a road spectrum diagram of a circulation working condition prestored into the singlechip or a requirement of a constant-speed working condition, so that a real road condition and an actual automobile condition can be reflected, and the current transient fuel consumption, the kilometer fuel consumption and the total stored fuel consumption can be displayed and output; data cannot be lost in a state of power failure, and the data can be put off and accumulated in a state of power on; and the tester is convenient to mount, safe and reliable, and on-automobile test is convenient.