Diesel engine exhaust has been identified to be highly carcinogenic. In order to improve the control of diesel engine exhaust emissions, the diesel engine oxidation catalyst (DOC) + catalytic diesel particulate filter (CDPF) + selective catalytic reduction catalyst (SCR) + NH3 oxidation catalyst (ASC) united technology has become the mainstream technology for catalytic aftertreatment. Perovskite oxides have emerged as a promising catalyst for NO oxidation and can be used as the DOC. Undoped La2MMnO6 (M=Co, Fe, Ni, Cu) double perovskites, A-site Ba-doping (La2-xBax) CoMnO6 (%Ba=0, 25%, 50%, 75%, 100%) perovskites and B-site Cu-doping La2Co1-yCuyMnO6 (y=0, 0.25, 0.50, 0.75, 1) double perovskites were prepared by a facile molten-salt synthesis method and examined by XRD, SEM, BET, in situ DRIFTS, and XPS. In addition, we calculated the B-site ionic magnetic moments of the double perovskites mu which were contributed by the effective Bohr magneton number n(p) of the B-site 3d transition metal ions, such as Mn3+, Mn4+, Co3+, Fe3+, Ni2+, and Cu2+. The correlations between the B-site ionic magnetic moments and the maximum NO conversion over all those double perovskites were also calculated. The B-site ionic magnetic moments has a strong positive correlation with the highest conversion rate of NO catalytic oxidation over all those double perovskites. That is, the higher the B-site ionic magnetic moments, the better the catalytic oxidation performance of NO over the double perovskites. So enhancing the B-site ionic magnetic moments by A-site doping is a method to improve the catalytic activity of NO oxidation over the perovskites. Increasing the B-site ionic magnetic moments is the key index to improve the catalytic activity of NO oxidation of the double perovskites by B-site doping.