Given the unpredictability and challenges brought about by the 2019 novel coronavirus (COVID‐19) pandemic, this study aimed to investigate the impact trend of the prolonged pandemic on the mental health of parents of children with autism spectrum disorder (ASD). The 8112 participants included parents of children with ASD and parents of typically developing (TD) children at two sites (Heilongjiang and Fujian province, China). The parents completed a set of self‐report questionnaires covering demographic characteristics, influences related to COVID‐19, COVID‐19 concerns and perceived behaviors, as well as the Connor‐Davidson resilience scale (CD‐RISC), self‐rating anxiety scale (SAS), and self‐rating depression scale (SDS) by means of an online survey platform. Data were collected by three cross‐sectional surveys carried out in April 2020 (Time 1), October 2020 (Time 2), and October 2021 (Time 3). The results of quantitative and qualitative comparisons showed that: (i) parents of children with ASD had lower levels of resilience, and more symptoms of anxiety and depression than parents of TD children at each time point (all P < 0.05); and (ii) there were significant time‐cumulative changes in resilience, anxiety, and depression among all participants (all P < 0.05). The logistic regression analyzes after adjusting for demographic characteristics revealed that the following factors were significantly associated with poor resilience and a higher rate of anxiety and depression in parents of children with ASD: time‐point, the effect of COVID‐19 on children's emotions and parents' emotions, changes in relationships, changes in physical exercise, changes in daily diet during the COVID‐19 pandemic, and COVID‐19‐related psychological distress. In conclusions, the parents did not report improvements in resilience, anxiety, or depression symptoms from Time 1 to Time 2 or 3, indicating that cumulative mental health issues increased when, surprisingly, the COVID‐19 restrictions were eased. The psychological harm resulting from the COVID‐19 pandemic is far‐reaching, especially among parents of children with ASD.