The technology of direct cracking of crude oil to produce ethylene effectively reduces the raw material cost and energy consumption of olefin plants, and quickly adapts to the transformation from fossil-fuels to fossil-materials. Based on the industrial experiment of crude oil cracking， the main distribution and content of impurities in the flows were studied, and the performance and stability of acetylene and MAPD selective hydrogenation catalysts were investigated. It was found that the organic S and As produced by the crude oil cracking have a much greater impact on the process than naphtha cracking. The development trends of the hydrogenation catalysts and the optimizations of processes are researched by analyzing the forms of organic S and As in the cracking gas and comparing their removal methods.