The invention discloses a multi-element nitralloy cored wire and an application method thereof in a reinforcing treatment technique of Q620D steel and belongs to the technical field of alloy material application. A wire core of the multi-element nitralloy cored wire comprises 15.5-24.9% of N, 27-48% of V, 18-32% of Si, 0.3-4% of Nb, 0.05-3% of Mn, 0.3-4.5% of B, 0.8-7.0% of Ti, 0.1-5.0% of Cr, 0-1.4% of C, 0-0.10% of P, 0-0.10% of S, and the balance Fe and trace impurities. According to the multi-element nitralloy cored wire and the application method thereof in the reinforcing treatment technique of the Q620D steel, multi-element nitralloy with the most proper components is designed and selected; beneficial elements are added, so that N is transferred to V, B and Nb easily, the V, B and Nb and N are combined easily, and positive correlation functions are achieved for steel performance reinforcement; the requirements of a microalloying reinforcing technique of the Q620D steel are completely meet, and the reinforcing effect of the multi-element nitralloy cored wire is brought into full play.