The present invention relates to a fuel injection pump having a separable plunger being capable of not only easily adjusting a timing and a form of fuel injection with a simple structure but also enabling fine pre-injection of an engine at high pressure, thereby assisting in warming up within an engine cylinder, such that complete combustion may occur when main fuel is entered. The fuel injection pump having the separable plunger includes a separable plunger of which outer circumference is slide coupled to an inside of the barrel such that a lower portion thereof is supported by an upper portion of the main plunger to enable upward and downward slide movement in association with the main plunger, wherein an injection timing control spiral step of which upper surface is formed in a spiral shape is protrudingly formed on the outer circumference thereof and a fuel passage is formed on one side of the outer circumference thereof including the injection timing control spiral step and
an elastic member having a lower portion elastically supported by the separable plunger and an upper portion inserted within the barrel to be supported by an upper surface of the barrel.