In contrast to its cubic zincblende phase under bulk form, GaAs nanowires usually adopt wurtzite structure. Surface reconstructions of wurtzite GaAs(1010)A and GaAs(1010)B surfaces have been investigated by using first-principles calculations. The results show that Ga-Ga and As-As dimmers are formed on GaAs (1010)B surface with surface energy 63.5×1020 meV/m2, while no reconstructions are formed on GaAs (1010)A with surface energy 40.6×1020 meV/m2. The relaxed GaAs WZ(1010)A surface has lower surface free energy and more stable.