The injection system of a fuel injection pump is provided. In the injection system of a fuel injection pump, a plunger performs a reciprocating slide motion in the axial direction inside of the plunger chamber of a barrel for compressing fuel. The plunger has a release groove and a control edge. A spill port is formed in the wall surface of the barrel. A damping groove is formed in the upper-part outer circumference of the control edge and provides a fine fuel flow path. The damping groove meets the spill port in advance to form the fine flow of fuel from the plunger chamber to the spill port before the control edge of the plunger meets the spill port to release pressure.