The present invention relates to a condenser tubes cleaning system for alleviating the common disadvantage of the prior arts includes a flow diverter, a first branch pipe, a second branch pipe, a three-way valve, a first one-way valve, a bypass pipe, a ball barrel, a liquid supply pipe, a cleaning ball supply pipe, a cleaning ball return pipe, a liquid return pipe, a second one-way valve, a normally open two-way valve, and a ball trap. Thus, the flow diverter is provided with the three-way valve, and the ball trap is provided with the normally open two-way valve, so that the flow diverter and the ball trap have a bypass function that the prior arts do not have, to maintain the constant flow rate in the main supply pipe and the main return pipe without increasing the electrical power load of the main circulating pump.