An exemplary lens module includes a barrel, a first lens fixedly disposed in the barrel, a second lens movably received in the barrel, and a pressure control device. The barrel includes a peripheral side wall. A hole is defined in the peripheral side wall. The first lens, the second lens, and the barrel together define a chamber. The chamber communicates with the hole. The pressure control device communicates with the hole so as to change the gas pressure of the chamber, thereby moving the second lens relative to the first lens.