The invention relates to a fuel-cleaning agent and a preparing method for the agent, which comprises by weight water 5 portions, triethanolamine 3 portions, methanol 13 portions, n-butanol 16 portions, ethylene glycol monobutyl ether 39 portions, ethylenediamine 7 portions, polyoxyethylene nonyl phenyl (4) ether 7 portions, fatty alcohol (3) ether 4 portions, dodeca ammonia poly oxy ethylene ether 3 portions, and oil thanol amide 3 portions. The agent is prepared by the following procedures: adding the 5 portions of water into a vessel; adding 39 portions of ethylene glycol monobutyl ether, 3 portions of triethanolamine, 12 portions of methanol, 16 portions of n-butanol while agitating; adding 7 portions of polyoxyethylene nonyl phenyl (4) ether after agitating, 3 portions of fatty alcohol (3) ether, 3 portions of dodeca ammonia poly oxy ethylene ether, and 7 portions of ethylenediamine; adding 3 portions of oil thanol amide after reaction; agitating, and keeping still. The invention has an obvious and rapid cleaning speed, is good for reducing oil consumption, improving fuel utilization, and reducing the emission of harmful substance in the tail gas, and is energy saving and environmental friendly.