The invention provides a system and method for automatically monitoring production line takt time. The system comprises a takt time monitoring module, a judging module, a counter and a takt time alarm module, wherein the takt time monitoring module is used for measuring and displaying the actual takt time of a station in real time and comparing the actual takt time with the target takt time of the station; the judging module is used for judging whether a part machined on the station is a first to-be-machined part or not, whether parts at the entrance of the station are sufficient or not and whether a station exit is blocked or not; when the actual takt time is larger than the target takt time and if the part machined on the station is not the first to-be-machined part, the parts at the entrance of the station are sufficient and the station exit is not blocked, 1 is added to the numerical value of the counter; if optional one of the above conditions is not satisfied, the counter resets; when the numerical value of the counter is not smaller than a preset value, the takt time alarm module gives out an alarm. The system has the advantages that the interference factor at the entrance, the interference factor at the exit and the interference factor that whether the part to be processed is the first part or not are fully considered and eliminated, automatic monitoring and alarm of the takt time are achieved, and false alarm is avoided.