The social isolation due to the COVID-19 pandemic exerts lasing impacts on people’s mental health. However, whether and how people’s pre-existing positive social relationships can serve as stable reserves to alleviate people psychological distress following the disaster remains unknown. To address the question, the current study examined whether pre-pandemic relationship satisfaction would predict post-pandemic COVID-19 anxiety through middle-pandemic perceived social support and/or gratitude using four-wave data in China (N = 222, 54.50% female, Mage = 31.53, SD = 8.17). Results showed that people’s COVID-19 anxiety decreased from the peak to the trough pandemic stage; perceived social support increased markedly from the pre-pandemic to the peak and remained stable afterwards, while relationship satisfaction remained unchanged throughout. Further, it was middle-pandemic perceived social support, but not gratitude, mediated the association between pre-pandemic relationship satisfaction and post-pandemic COVID-19 anxiety, indicating perceived social support played a more crucial role than gratitude in this process. Last, it is suggested to distinguish perceived social support from gratitude as two different components of social interactions.