Improving the jet reactor's mixing performance is critical and challenging. In this paper, a new type of vortex-inducing T-jet reactor proposed by researchers is studied. By designing the staggered inlet structure of the T-jet reactor, the vortex is induced in the flow field in the mixing channel to improve the mixing effect. Flow regimes and mixing characteristics in the vortex-inducing T-jet reactor were investigated through numerical simulations (CFD) at 30 ≤ Re ≤ 600. Results show that the staggered inlet channel induces vortices successfully, and the engulfment flow regime occurs at lower Reynolds numbers, thus promoting the mixing. The generation and evolution of vortex structures in the reactor were focused on. It was found that in the unsteady engulfment flow, the two fluids cross each other, which makes the vortex structure constantly twist and merge, which greatly improves the mixing effect. At larger Reynolds numbers, many attached small vortices are generated around the central vortex structure, and these vortices are wound together with the high-speed rotation of the central vortex, avoiding the unsteady symmetric flow pattern with a poor mixing effect. Finally, it is found that the mixing performance of the vortex-inducing T-jet reactor is greatly improved under all regimes.