The invention relates to coke inhibitor for ethylene cracking, which comprises the following component by weight percentage: 20% to 60% of sulfur-containing compound, 5% to 10% of passivator, 1% to 10% of film-forming agent, 5% to 15% of polymerization inhibitor, 1% to 10% of decoking agent and 25% to 45% of solvent, wherein the sulfur-containing compound is particularly dialkyl disulfide, dialkyl sulfide, di-alkylphenol sulfide, diphenyl sulfide, diphenyl disulfide, thiophene or thioxene; and the passivator is particularly triphenyl phosphate, triethyl phosphate, di-octyl-phenyl-phosphate, tributyl phosphate, thiophosphate trilaurate, diethyl-phosphorodi-thioate or triacyl piperidine phosphate, and the passivator is preferably triphenyl phosphate or di-octyl-phenyl-phosphate. The coke inhibitor of the invention for ethylene cracking is capable of effectively relieving the coking condition of an ethylene cracking tube, ensuring the good coke-inhibiting effect, obviously increasing the operation cycle of cracking and reducing the air-decoking time. Therefore, the coke inhibitor of the invention has wide applicable range in the coke inhibition of gaseous light dydrocarbon and naphtha.