Background: Children with autism spectrum disorder (ASD) are susceptible to excessive electronic screen media (ESM) use. This study aimed to evaluate the effectiveness of a parent training programme in improving the screen time and social functioning of children with ASD. Methods: This pre-/post-test quasi-experimental study involved parents by providing them with structured education based on the American Academy of Pediatrics (AAP)’ screen time recommendations. In total, 259 children with ASD aged 3 years old–12 years old were eligible. Of those children, 26 were excluded due to comorbidities or taking medications. Additionally, 28 parents participated. Children’s screen time were recorded, and social behaviour was scored using the Social Responsiveness Scale pre- and post-intervention. Results: There were significant reductions in the average daily screen time of children with ASD after their parents attended the training programme (-51.25 min; 95% CI: -78.40, -24.10). In subgroups with reduced screen time, the treatment effect of the intervention was significant in improving the social responsiveness total score (-3.09; 95% CI: -5.96, -0.22), the social communication scale (-3.64; 95% CI: -5.91, -1.36) and the restricted interest and repetitive behaviour (RRB) scale (-5.27; 95% CI: -10.29, -0.25). Conclusion: Parental training is effective in reducing screen time and improving social functioning in children with ASD.