By means of molecular dynamics (MD) simulations, the melting mechanism of thin W(111) and W(110) planes with free surfaces has been studied with the modified analytic embedded-atom method (MAEAM). Firstly, the results obtained by calculating the temperature dependence of mean square displacement (MSD) indicate that the influence of surface and anharmonic effect on the microstructure and properties of planes are significant and the vibration of atoms locating in the surface region is anisotropic. Then, according to providing further investigation into the temperature dependence of the atomic density function (ADF) and structural factor (SF) of the given atomic planes, it is found that the melting mechanisms and processes of both membranes are different. For the W(111) plane, the free surface plays an important role in the melting transition. The W(111) plane entirely becomes disordering at 3700 K which is in agreement with the calculated melting temperature. The fitted relation between the fraction of the disordered atom and the temperature demonstrates that the premelting-melting transition temperature is about 3550 K. Instead, the W(110) plane is melted when the temperature reaches 4000 K, which is so-called superheating. And the melting transition of this plane relies strongly on the anharmonic effect.