The invention discloses an engine rotational 
inertia measuring device. The engine rotational 
inertia measuring device comprises a 
machine body, a driving mechanism, a belt transmission 
assembly and aconnecting 
flange connected with an output end 
flange of an engine to be measured; the 
machine body comprises two adjacently arranged bases and three supporting seats; the driving mechanism comprisesa motor and a 
reducer which are connected in a transmission mode, and is placed on the bases and the supporting seats; the belt transmission 
assembly comprises a belt transmission mechanism, a belt tensioning mechanism and two rotating shafts, the two rotating shafts can be rotatably connected with two belt pulleys and the belt tensioning mechanism through four bearings, the first rotating shaft is coaxially and fixedly connected with the output end of the 
reducer, and the second rotating shaft is fixedly disposed at the center of the connecting 
flange. The 
power output by the driving mechanism can be transmitted to the output end flange of the engine to be measured under the action of the belt transmission 
assembly, and by measuring the change conditions of the rotational speed torque ofan engine output shaft, the rotational 
inertia of the engine to be measured can be accurately measured. The engine rotational inertia measuring device has a compact structure, convenient assembly anddisassembly, high practicability and convenient popularization and use.