The invention provides corrosion inhibitor for carbon steel in the oil field acid environment, and particularly relates to preparation and application of low-toxicity and efficient corrosion inhibitor for restraining corrosion of carbon steel and products of the carbon steel in oil field acid pickling liquid or a saturated CO2 medium. According to the preparing method of the corrosion inhibitor, 3-phenylpropionic acid and diethylenetriamine are subjected to the dehydration reaction, and the phenylpropionic acid imidazoline ramification is obtained. According to the product, comprehensive corrosion and local corrosion is prevented from being generated in the process that the carbon steel makes contact with the acid pickling liquid or the CO2 medium. The compound does not serve as metal corrosion inhibitor at current. By adoption of the corrosion inhibitor, production is simple and convenient, toxicity is small, the inhibition rate is high, corrosion damage to the carbon steel from the acid pickling liquid or CO2 can be effectively restrained, and wide application prospects are achieved. The steps are simple, operation is convenient, and practicability is high.