A ball screw adapted to detecting coolant liquid includes a screw, a nut, a plurality of sealing members, a sensor, a signal processing unit and a cover. The nut includes a main body and an end surface, and a through-hole and a flow channel are disposed on the main body. The nut is threadedly disposed on the screw via the through-hole. A plurality of openings are disposed on the end surface, and the openings communicate with the flow channel. The sealing members are disposed in the plurality of openings. The sensor is disposed on one of the sealing members to detect a pressure of the coolant liquid and output an original signal. The signal processing unit is electrically connected to the sensor to receive the original signal and convert the original signal to a digital signal. The cover is disposed on the sensor and fixed to the nut.