Abstract: In order to reduce emissions of diesel engines, hydrogen for fuel of heavy-duty diesel engines paid more attention in recent years. Effect of the addition of hydrogen on the emissions of NOx and PM at different proportion (the highest volume proportion of the hydrogen is 7% of hydrogen air mixture in inlet pipe) into 2004 Mack MD11 diesel engine have been conducted. Research showed that the addition of hydrogen on NOx emission characteristics had different effects with the increase of hydrogen added in various load. And a change from NO to NO2 had been found. It was found that emission of NOx related to the variable-geometry gas turbine (VGT) and exhaust gas recirculation(EGR). And NOx emission was not significantly increased after adding hydrogen gas even at large or full load operating condition, which was mainly attributed to the EGR of the diesel engine, and the EGR rate was increased as the load increasing. Research also showed that adding hydrogen can reduce PM emission under different load conditions.