The invention provides a composite gas hydrate inhibitor. The composite gas hydrate inhibitor is composed of a kinetic inhibitor, a synergist and cyanamide sulfate according to a mass ratio of (1-4):1: 1. The kinetic inhibitor comprises at least two of a terpolymer, polyvinyl pyrrolidone and polyvinyl caprolactam. The terpolymer is a vinyl pyrrolidone/vinyl caprolactam/dimethyl aminoethyl methacrylate copolymer. The invention also provides a preparation method and use of the composite gas hydrate inhibitor. The composite gas hydrate inhibitor has obvious inhibitory effects, a small dosage, aconcentration of 0.2-2% and small pollution to the environment.