The invention discloses a plunger and barrel assembly of an oil injection pump of a marine diesel engine. The plunger and barrel assembly comprises a sleeve with oil inlet holes, a plunger matched with the sleeve, an oil scraping device and a sealing ring on the outer surface of the sleeve, wherein the oil inlet holes comprise an inner hole, a trumpet-shaped middle hole and a trumpet-shaped outerhole; the oil scraping device is arranged at the tail end of the sleeve through an annular nut and comprises two oil scraping rings made of a carbon fiber PRFE material and a spacer ring between the two oil scraping rings; the oil scraping rings are provided with tapered inner walls, and small inner diameter ends of the oil scraping rings are opposite to the backspacing direction of the plunger and tightly embrace the plunger; the end face of each small inner diameter end of the oil scraping rings is an inclined plane; and the outer edges of the oil scraping rings are provided with arc annular grooves with sealing rings. The plunger and barrel assembly of the oil injection pump of the marine diesel engine can effectively reduce the oil consumption and the exhaust of a diesel engine, meet the requirement on the oil injection pump of the marine diesel engine, prevent fuel oil leakage of a fit clearance of the plunger and the sleeve from polluting the lubricating oil of a cam shaft system and prolong the service life of the cam shaft system.