To improve the tribological properties of lubricant oil and enhance the stability and security of mechanical equipment under severe working conditions, the friction reduction and anti-wear performance of nano-calcium borate (CaB) and molybdenum dialalkyl dithiophosphates (MoDDP) composite additives were studied using four-ball tester and block on ring tester. The results showed that the prepared nano-CaB was a nanosheet with irregular shape and the average size was 50-150 nm. After oleic acid modification, it showed good dispersion stability in base oil. Both nano-CaB and MoDDP could significantly improve the lubrication effect of lubricant oil. With the increasing of nano-CaB and MoDDP mass fraction, the friction coefficient and grinding spot diameter firstly decreased and then increased. The optimal adding mass fraction of nano-CaB and MoDDP was 2.0% and 1.5%, respectively. Compared with single addition of CaB and MoDDP, compound CaB/MoDDP could further improve the friction reducing and anti-wear performance of lubricant oil. The optimal mass fraction ratio of MoDDP and CaB is 1.5%∶3.0% that showed the smallest friction coefficient and grinding spot diameter, and the highest maximum nonseizure load. It also showed excellent lubrication effect under low speed and heavy load condition.