The properties of the Anti-Reflection coated (AR-coated) GaAs diode lasers are investigated systematically in Littrow configuration. The tuning range of about 30 GHz is obtained without any mode-hops by the current compensation technique. Using a heterodyne detection technique, the linewidth of the AR-coated ECDL is measured, which is about 120 kHz. We also investigate the intensity noise of the AR-coated ECDL as a function of the current and the wavelength. The relations between the intensity noise of the ECDL and the driving current and wavelength are obtained and analyzed. This laser system can be used in many areas, such as atomic physics, laser spectroscopy and quantum optics, etc.