Abstract: To address the precise control requirements for swirl ratios in highly boosted diesel engines, a three-dimensional transient numerical simulation model was constructed based on a tangential straight-through intake duct structure. The dynamic influence mechanism of asymmetric intake valve lift control on in-cylinder swirl characteristics was systematically revealed. It was found that a four-stage evolution pattern of the swirl ratio was shown during the intake process: rapid establishment of swirl during the overlap period−decline after the exhaust valve closes （EVC）−re-raise at high lift−slow descent during the return stroke. The outlet far from the air passage inlet （distant from inlet exit, DIE） continuously promoted the development of the countercurrent swirl. Adjusting the lift of the DIE valve using an initial steep rise scheme increased the swirl ratio by 23.4%, but the decline after EVC was significant. The outlet close to the air passage inlet （close to inlet exit, CIE） inhibited the countercurrent swirl in the first three stages, but only the return stroke stage had a promoting effect. Shortening the initial lift of the CIE valve alone could induce an reverse swirl environment, resulting in a 50.1% decrease in the swirl ratio. Since the bottleneck of a significant increase in the swirl ratio cannot be broken through by single valve adjustment, a non-symmetric valve gradient collaborative scheme was proposed. The DIE valve adopted an initial steep rise lift, strengthening the establishment of countercurrent swirl during the overlap period. A high lift was adopted on the CIE valve throughout the stroke, suppressing the reverse jet and reducing the turbulent energy dissipation. The swirl ratio at the intake end significantly increased by 65.6%, compared to that of the original engine by this scheme.