A novel fused heterocyclic quaternary ammonium salt (BQD) corrosion inhibitor was developed using the onepot synthesis method, which employed quinoline and benzyl chloride. The one-pot synthesis method was easy to operate and successfully increased the effective BQD content to 50 %, aiming to provide an effective acidic corrosion inhibitor. The corrosion inhibition performance of BQD on N80 steel sheets in 20 % HCl solution was evaluated by weight loss and electrochemical tests. The synergistic inhibition between BQD and different compounding agents was investigated. The results indicated that BQD possessed good inhibition performance at 363 K. A corrosion inhibition rate of 99.17 % was achieved at an ultra-low concentration (0.05 % BQD). In addition, a synergistic performance was observed when combining BQD with either KI or urotropine. The system of BQD with urotropine presented the best inhibition performance, and the corrosion rate was further reduced to 2.87 g·m− 2 ·h− 1 . The adsorption of the inhibitor system on the N80 steel surface was followed by Langmuir adsorption isotherm, which adsorbed on the N80 steel surface by chemical adsorption. The inhibition mechanism of BQD on N80 steel was studied by scanning electron microscopy (SEM) measurement, energy dispersive spectroscopy (EDS) analysis, contact angle determination, and molecular dynamics (MD) simulation. BQD can be adsorbed parallel to the surface of a steel sheet by using a conjugate plane consisting of a five-membered nitrogen-containing heterocycle and two six-membered rings on either side of the five-membered heterocycle as the reference plane. Therefore, BQD forms an adsorption protection film on the steel sheet surface, which can effectively slow down metal corrosion by acid solution.