We demonstrate an atomic-sized Pd tunneling junction memory that can operate in a vacuum, N2, or ambient environment. Calculation based on quantum point contact model indicated the size of the tunneling gap is between 0.1 to 2nm, and the switching between high resistance state and low resistance state is achieved by a migration of a few atoms near the junction. The device\'s RESET speed is 25ns, and the ON/OFF ratio is 2 to 103, with an endurance of 1000 cycle life. We proposed a phenomenological model to explain the imperfection of device performance, which could be useful for circuit design.