A direct-fired plunger hydraulic pump, comprising a combustor (1), a high-temperature heat exchanger (2), a steam chamber (3), at least one cylinder plunger mechanism (10), a steam refrigerator (15) and a control system, wherein the high-temperature heat exchanger (2) is connected with the combustor (1) through a pipe; the steam chamber (3) is a sealed container, in which a water nozzle (4) is arranged above the high-temperature heat exchanger (2); the cylinder plunger mechanism (10) is mounted above the steam chamber (3) and mainly consists of a cylinder (20) and a plunger (21); a piston of the cylinder (20) is connected with a piston of the plunger (21) through a mandril (30) with a reset mechanism; an inlet valve (22) communicated with the steam chamber (3) is provided at the bottom end of the cylinder (20), and an exhaust valve (23) is provided on a side wall of the cylinder (20); an oil outlet and an oil inlet are provided at the top end of the plunger (21); the exhaust valve (23) is connected with the steam refrigerator (15) through an exhaust pipe (14); and the refrigerator (15) is connected with a water tank (8). The direct-fired plunger hydraulic pump has the advantages of simple structure, energy conservation and high efficiency, and most of the thermal energy generated by fuel provides hydraulic machines with power by heat exchange so that the energy consumption is small.