The invention provides a power generation device of an alkali metal thermoelectric direct converter taking residual heat of a diesel engine as a heat source. Exhaust gas exhausted by an exhaust pipeline of the diesel engine is connected with a heat transfer working medium flowing-in port on a heat exchanger, the heat exchanger is arranged in a heat accumulator, heat-absorbing materials of the heat accumulator are arranged around the heat exchanger, a heat-insulating sealing device is arranged between the heat exchanger and the heat accumulator, an alkali metal thermoelectric conversion device is connected with the heat accumulator through an interface, and heat in the heat accumulator is conducted into the alkali metal thermoelectric conversion device through a heat output interface of the heat accumulator and a heat input interface of the alkali metal thermoelectric conversion device, thereby leading an alkali metal working medium in the alkali metal thermoelectric conversion device to achieve the requirements of working conditions; furthermore, current is produced by the alkali metal thermoelectric conversion device, and the current is flowed out through a positive pole of the alkali metal thermoelectric conversion device and returns to a negative pole after flowing by a load for doing work. The exhaust gas of the diesel engine is taken as the heat source of the alkali metal thermoelectric direct converter, thereby effectively utilizing resources and improving the utilization efficiency of energy.