An electrically-controlled monolithic high-pressure oil pump for a marine low-speed engine, comprising: a pump body, wherein the pump body is provided with a center hole along an axial direction; a pump cover, wherein the pump cover is mounted on an upper end surface of the pump body; an oil inlet-outlet valve assembly, a plunger couple, a plunger spring, a lower spring seat assembly and a guide piston assembly, all of which are assembled in the center hole of the pump body; and an electrically-controlled proportional valve, wherein the electrically-controlled proportional valve is assembled on a side surface of the pump body, wherein the oil inlet-outlet valve assembly comprises: an oil inlet valve assembly and an oil outlet valve assembly; the oil inlet valve assembly comprises: an oil inlet valve seat, an oil inlet valve and an oil inlet valve spring; the oil inlet valve is mounted in a center hole of the oil inlet valve seat, the oil inlet valve spring is restrained between the oil inlet valve and a bore wall of the oil inlet valve seat, and the oil inlet valve is configured to form a conical seal with the oil inlet valve seat under compression of the oil inlet valve spring; the oil outlet valve assembly comprises: an oil outlet valve seat, an oil outlet valve, an oil outlet valve spring and an oil outlet valve spring seat; the oil outlet valve spring seat is mounted on an upper end of the oil outlet valve seat, the oil outlet valve is mounted in a center hole of the oil outlet valve seat, the oil outlet valve spring is restrained between the oil outlet valve and the oil outlet valve spring seat, and the oil outlet valve is configured to form a conical seal with the oil outlet valve seat under compression of the oil outlet valve spring; a high-pressure oil outlet chamber is formed between the oil outlet valve seat and the oil inlet valve seat; a high-pressure oil chamber is formed in the plunger couple, and the high-pressure oil chamber communicates with the high-pressure oil outlet chamber through a first oil hole of the oil inlet valve on the oil inlet valve seat; and the electrically-controlled proportional valve communicates with an oil inlet hole of the oil inlet valve seat through the first oil hole on the pump body, and the oil inlet hole of the oil inlet valve seat is configured to communicate with or be disconnected from the high-pressure oil chamber; characterized in that the electrically-controlled proportional valve is provided thereon with a cooling circulation oil passage, wherein cooling oil from a cooling oil passage of the pump body, after being injected into the cooling circulation oil passage, is returned to the cooling oil passage of the pump body. a pump body, wherein the pump body is provided with a center hole along an axial direction; a pump cover, wherein the pump cover is mounted on an upper end surface of the pump body; an oil inlet-outlet valve assembly, a plunger couple, a plunger spring, a lower spring seat assembly and a guide piston assembly, all of which are assembled in the center hole of the pump body; and an electrically-controlled proportional valve, wherein the electrically-controlled proportional valve is assembled on a side surface of the pump body, wherein the oil inlet-outlet valve assembly comprises: an oil inlet valve assembly and an oil outlet valve assembly; the oil inlet valve assembly comprises: an oil inlet valve seat, an oil inlet valve and an oil inlet valve spring; the oil inlet valve is mounted in a center hole of the oil inlet valve seat, the oil inlet valve spring is restrained between the oil inlet valve and a bore wall of the oil inlet valve seat, and the oil inlet valve is configured to form a conical seal with the oil inlet valve seat under compression of the oil inlet valve spring; the oil outlet valve assembly comprises: an oil outlet valve seat, an oil outlet valve, an oil outlet valve spring and an oil outlet valve spring seat; the oil outlet valve spring seat is mounted on an upper end of the oil outlet valve seat, the oil outlet valve is mounted in a center hole of the oil outlet valve seat, the oil outlet valve spring is restrained between the oil outlet valve and the oil outlet valve spring seat, and the oil outlet valve is configured to form a conical seal with the oil outlet valve seat under compression of the oil outlet valve spring; a high-pressure oil outlet chamber is formed between the oil outlet valve seat and the oil inlet valve seat; a high-pressure oil chamber is formed in the plunger couple, and the high-pressure oil chamber communicates with the high-pressure oil outlet chamber through a first oil hole of the oil inlet valve on the oil inlet valve seat; and the electrically-controlled proportional valve communicates with an oil inlet hole of the oil inlet valve seat through the first oil hole on the pump body, and the oil inlet hole of the oil inlet valve seat is configured to communicate with or be disconnected from the high-pressure oil chamber; characterized in that the electrically-controlled proportional valve is provided thereon with a cooling circulation oil passage, wherein cooling oil from a cooling oil passage of the pump body, after being injected into the cooling circulation oil passage, is returned to the cooling oil passage of the pump body.