A fuel injection system for an internal combustion engine, the internal combustion engine including: a port injector configured to inject fuel into an intake port; and an in-cylinder injector configured to inject fuel into a cylinder, the in-cylinder injector including a needle valve, and the in-cylinder injector being able to execute partial lift injection while the needle valve is not fully opened, the fuel injection system comprising at least one electronic control unit configured to a) control the port injector and the in-cylinder injector by controlling energization of the port injector and the in-cylinder injector, b) set the number of times that maximum partial lift injection is executed in one fuel injection cycle, based on a pressure of the fuel supplied to the in-cylinder injector such that an injection amount of the maximum partial lift injection in one fuel injection cycle is equal to or less than a total injection amount for one injection cycle, the maximum partial lift injection being included in the partial lift injection, and the maximum partial lift injection being injection that requires the longest energization time of the in-cylinder injector, in the partial lift injection, c) cause the in-cylinder injector to execute the maximum partial lift injection the set number of times, and d) cause the port injector to inject the fuel in an amount equal to a shortfall with respect to the total injection amount, wherein the amount of fuel injected by the port injector is calculated by subtracting the injection amount of the maximum partial lift injection per injection stroke from the total injection amount. a port injector configured to inject fuel into an intake port; and an in-cylinder injector configured to inject fuel into a cylinder, the in-cylinder injector including a needle valve, and the in-cylinder injector being able to execute partial lift injection while the needle valve is not fully opened, the fuel injection system comprising at least one electronic control unit configured to a) control the port injector and the in-cylinder injector by controlling energization of the port injector and the in-cylinder injector, b) set the number of times that maximum partial lift injection is executed in one fuel injection cycle, based on a pressure of the fuel supplied to the in-cylinder injector such that an injection amount of the maximum partial lift injection in one fuel injection cycle is equal to or less than a total injection amount for one injection cycle, the maximum partial lift injection being included in the partial lift injection, and the maximum partial lift injection being injection that requires the longest energization time of the in-cylinder injector, in the partial lift injection, c) cause the in-cylinder injector to execute the maximum partial lift injection the set number of times, and d) cause the port injector to inject the fuel in an amount equal to a shortfall with respect to the total injection amount, wherein the amount of fuel injected by the port injector is calculated by subtracting the injection amount of the maximum partial lift injection per injection stroke from the total injection amount. a) control the port injector and the in-cylinder injector by controlling energization of the port injector and the in-cylinder injector, b) set the number of times that maximum partial lift injection is executed in one fuel injection cycle, based on a pressure of the fuel supplied to the in-cylinder injector such that an injection amount of the maximum partial lift injection in one fuel injection cycle is equal to or less than a total injection amount for one injection cycle, the maximum partial lift injection being included in the partial lift injection, and the maximum partial lift injection being injection that requires the longest energization time of the in-cylinder injector, in the partial lift injection, c) cause the in-cylinder injector to execute the maximum partial lift injection the set number of times, and d) cause the port injector to inject the fuel in an amount equal to a shortfall with respect to the total injection amount, wherein the amount of fuel injected by the port injector is calculated by subtracting the injection amount of the maximum partial lift injection per injection stroke from the total injection amount.