Background The ability to regulate emotion effectively plays a key role in child psychosocial development and mental health. The current study examines the effect of cognitive training for executive function on emotion regulation in Chinese preschool children, and further investigate the underlying mediating mechanisms. Methods A cluster randomized control trial design with pre-test and post-test was conducted in 61 preschool children aged 3-6 years in China. The intervention group consisted of 30 children who received eight cognitive training sessions on executive function, while the control group consisted of 31 children who did not receive any psychological training. Children's executive function was measured individually via five laboratory tasks both in the pre-test and post-test. Adaptive and maladaptive emotion regulation strategies were coded in emotion-elicit contexts. Results Intervention group outperformed control group in working memory and inhibitory control. Children in the intervention group exhibited increased use of adaptive emotion regulation strategies and decreased use of maladaptive emotion regulation strategies than children in the control group. Mediation analyses indicated that there were significantly indirect effects of Intervention Condition on the gain scores of adaptive and maladaptive emotion regulation strategies through the gain score of inhibitory control. Conclusions Executive function training effectively promotes working memory, inhibitory control and the use of adaptive emotion regulation strategies, and reduces the use of maladaptive emotion regulation strategies. In addition, executive function training improves the use of adaptive and maladaptive emotion regulation strategies through the enhancement of inhibitory control capacity.