An ASED-MO method has been applied to investigate the N2 chemisorption on Cr(110) surface. The results show that N2 chemisorbs parallelly on the 4-fold site with N-N axis parallel to [110] direction. Different from the tranditional σ-donation and π weak backbonding concepts, the N2 chemisorption on Cr(110) has both the 3 σg and 1 πμ donations of 0.97 and 0.54 electrons. At the same time, the backbonding to the 1 πg orbital increases to 1.83 electrons. Both these factors make the lying-down orientation being favored over the upright orientation. Furthermore, the N-N bond length strenches 17%, the N-N bond order decreases to below 1, and the dissociation barrier is only about 0.15 eV. All the above calculation results are in good agreement with relevant experiments.