The developed loading device with opened hydrostatic circuit for measurement of speed and dynamic characteristics of the tractor engine by power take off is presented. This loading device may also be used as a portable type for field measurement. At present for development of these loading devices controlled hydrogenerators and electro-hydraulic proportional pressure valves directed by computer may by used to adjust geometrical volume of the hydrogenerator from zero to maximum value. There is a possibility to built these devices which consist of one hydrogenerator and one by-pass valve for the maximum power of internal combustion engine 420 kW which is sufficient from the point of view of practical need. Thus optional loading regime may be used according to the tractor engine horsepower to achieve the required accuracy of measurement.