The invention discloses a large mineral track tensioning device of a hydraulic excavator, relating to a hydraulic excavator and solving the problems that the traditional tensioning device has poor buffer effect and potential safety hazard. The large mineral track tensioning device consists of a tensioning oil cylinder and a buffer device, wherein the buffer device is a buffer oil cylinder and arranged in the same cylinder body together with the tensioning oil cylinder; the buffer oil cylinder is arranged at the guide wheel side; a rodless cavity of the buffer cylinder is formed between a piston rod of the buffer cylinder and the cylinder body; the front end of the cylinder body is connected with a cylinder cover of the buffer cylinder through bolts; a two-way inserted sliding valve is integrated at the bottom of the buffer oil cylinder and communicated with a control oil port which is connected with a main pump control valve; the rodless cavity of the buffer cylinder is communicated with the buffer oil port which is connected with an energy accumulator; the tensioning oil cylinder is arranged at the driving wheel side; a rodless cavity of the tensioning oil cylinder is formed between a piston rod of the tensioning oil cylinder and a cylinder body; the rear end of the cylinder body is connected with a cylinder cover of the tensioning cylinder through bolts; and the rodless cavity of the tensioning oil cylinder is communicated with a tensioning oil port.