Tomato is a leading vegetable in modern agriculture, and with global warming, drought has become an important factor threatening tomato production. Mitogen-activated protein kinase 3 (MAPK3) plays an important role in plant disease and stress resistance. To clarify the downstream target proteins of SlMAPK3 and the mechanism of stress resistance in tomato, this study was conducted with the SlMAPK3-overexpressing lines OE-1 and OE-2 and the CRISPR/Cas9-mediated mutant lines slmapk3-1 and slmapk3-2 under PEG 6000-simulated drought. The results of yeast two-hybrid (Y2H), pull-down, and coimmunoprecipitation (Co-IP) assays confirmed that SlASR4 (NP_001269248.1) interacted with SlMAPK3. Analyses of the SlASR4 protein structure and SlASR4 expression under PEG 6000 and BTH stress revealed that SlASR4 has a highly conserved protein structural domain involved in the drought stress response under PEG 6000 treatment. The function of the SlASR4 and SlMAPK3 downstream target protein, in drought resistance in tomato plants, was identified by virus-induced gene silencing (VIGS). This study clarified that SlMAPK3 interacts with SlASR4 to positively regulate drought resistance in tomato plants.