The overall design of Z6170ZLCZ/S-8 dual fuel engine is introduced focusing on the inlet and control system of natural gas, as well as how to realize duel fuel combustion.Comparison was conducted between the two modes of pure diesel and dual fuel, and the results show that the replacement rate of diesel with natural gas could reach as high as 75%, and the average fuel replacement rate is 70%, and other performance parameters have all reached the design requirements.