A blood pressure device includes a first blood pressure measuring device, a second blood pressure measuring device, and a controller. The first blood pressure measuring device is to be worn on a first position of a wrist so as to obtain a first blood pressure information of the first position. The second blood pressure measuring device is to be worn on a second position of the wrist so as to obtain a second blood pressure information of the second position. The controller is electrically coupled to the first blood pressure measuring device and the second blood pressure measuring device so as to adjust tightness between the expanders and the user's skin, respectively. The controller receives, processes, and calculates a pulse transit time between the first blood pressure information and the second blood pressure information, and the controller obtains at least one blood pressure value based on the pulse transit time.