Nodal line semimetal (NLS) is a new quantum state hosting one-dimensional closed loops formed by the crossing of two bands.The so-called type-Ⅱ NLS means that these two crossing bands have the same sign in their slopes along the radial direction of the loop,which requires that the crossing bands are either right-tilted or left-tilted at the same time.According to the theoretical prediction,MgaBi2 is an ideal candidate for studying the type-Ⅱ NLS by tuning its spin-orMt coupling (SOC).High-quality Mg3Bi2 films are grown by molecular beam epitaxy (MBE).By in-situ angle resolved photoemission spectroscopy (ARPES),a pair of surface resonance bands around the (Γ) point are clearly seen.This shows that Mg3Bi2 films grown by MBE are Mg(1)-terminated by comparing the ARPES spectra with the first principles calculations results.Moreover,the temperature dependent weak anti-localization effect in Mg3Bi2 films is observed under magneto-transport measurements,which shows clear two-dimensional (2D) e-e scattering characteristics by fitting with the Hikami-Larkin-Nagaoka model.Therefore,by combining with ARPES,magneto-transport measurements and the first principles calculations,this work proves that Mg3Bi2 is a semimetal with topological surface states.This paves the way for MgaBi2 to be used as an ideal material platform to study the exotic features of type-Ⅱ nodal line semimetals and the topological phase transition by tuning its SOC.