Disclosed is a park plug, which has a conductive plate constituting a side electrode, and a slot is defined through the conductive plate, so that no dead zone is present around the spark plug for a fuel injection system and thereby achieving more complete combustion. The spark plug is threadingly fit into a combustion chamber of an engine and employs a high-voltage electric current to generate spark for ignition and thus enabling combustion and explosion to generate power for driving movement of cylinders. Thus, by providing a slot in the conductive plate of the side electrode, a mixture gas of fuel and air inside the combustion chamber can be completely spread around the spark plug to thereby enhance combustion efficiency. This not only reduces fuel consumption and enhances horsepower, but also eliminates jamming of an injection engine due to less carbon deposition.