Abstract: To explore the predation potential of Sphedanolestes impressicollis on Spodoptera litura, the predatory function and searching effect of the 4th instar nymphs of S. impressicollis on the 1st, 2nd and 3rd instar larvae of Spodoptera litura, the interference effect of different densities of the 4th instar nymphs of S. impressicollis on its predatory function on S. litura, and the influence of predatory space size on the predatory function of the 4th instar nymphs of S. impressicollis on the 1st, 2nd and 3rd instar larvae of S. litura were studied in laboratory. The results showed that the predatory functional response of the 4th instar nymphs of S. impressicollis on young larvae of S. litura was consistent with Holling Ⅱ model, and their instantaneous attack rates on the 1st, 2nd and 3rd larvae of S. litura were 0.979, 0.999 and 0.164 with the treatment time of 0.013, 0.020 and 0.018 d and the maximum daily predatory capacities of 74.5, 51.2 and 6.1 larvae, respectively. The searching effect of the 4th instar nymphs of S. impressicollis was negatively correlated with the density of young larvae of S. litura, while the predation rate of the 4th instar nymphs of S. impressicollis on the larvae of S. litura decreased with the increase of their density. When preying on the 1st instar larvae of S. litura, the density of the 4th instar nymphs of S. impressicollis had the most interference effect on their preying ability. Therefore, the 4th instar nymphs of S. impressicollis have certain predation potential on the young larvae of S. litura, and can be used for the green control of young larvae of S. litura in tobacco fields.