An oil injector, inside which a positive temperature coefficient ceramics heating material is arranged, mainly comprises an injector needle valve, an injector needle valve body, an injector body, an injector tappet, an injector pressure-adjusting spring, a round heat transfer pipe inside the injector body, positive temperature coefficient heating ceramics inside the injector body, an insulated jacket inside the injector body, a round heat transfer pipe inside an oil inlet bolt, positive temperature coefficient heating ceramics inside the oil inlet bolt, an insulated jacket inside the oil inlet body, and so on. Positive temperature coefficient heating ceramics is arranged inside the oil inlet bolt and the oil injector, heats the diesel oil with a self-controlling temperature via the heat transfer pipes, and is insulated through the insulated jacket. The invention provides an oil injector used for diesel heating at the self-controlling temperature during the coal start and warm-up courses. The heating temperature will not exceed the boiling point of diesel oil. Less heating is needed, and the heating is quicker, so the diesel emission can be effectively improved and the cold-start performance can be promoted.