An object location estimating method with a timestamp alignment function is applied to an object location estimating device. The object location estimating method includes acquiring a plurality of first frames from a first camera, setting a first predetermined point of time, defining a first previous frame and a first next frame closest to the first predetermined point of time from the plurality of first frames, acquiring a first previous coordinate value of an object within the first previous frame and a first next coordinate value of the object within the first next frame, and utilizing the first previous coordinate value and the first next coordinate value to compute a first estimation coordinate value of the object at the first predetermined point of time.