Since the outbreak of COVID-19, researchers worldwide have focused more on the issue of secondary traumatic stress (STS) experienced by nurses. This stress has an adverse effect on the health of nurses and the quality of nursing care, potentially undermining the stability of the nursing team and hindering the ability to meet the growing demand for nursing services. The impact of the COVID-19 pandemic, and the rise in global demand for ICU nursing, has placed a significant strain on ICU nurses, severely damaging their mental and physical health. Notably, ICU nurses also face high levels of moral distress, and moral resilience can effectively alleviate this distress and improve the quality of care. This study aimed to examine the levels of moral resilience and STS among ICU nurses, to explore their relationship and identify the factors influencing STS. This cross-sectional study involved 229 ICU nurses from two tertiary hospitals in Xi'an, China, who participated between November and December 2023. The data were collected through email using anonymous electronic questionnaires, encompassing a self-designed demographic- and work-life-related characteristic questionnaire; the Rushton Moral Resilience Scale; and the Secondary Traumatic Stress Scale. Descriptive statistics, t-tests, analysis of variance and hierarchical regression analysis were performed to analyse the data. The findings of the study indicated that ICU nurses' moral resilience and STS scores were at an intermediate level. Hierarchical regression analysis indicated that STS was negatively correlated with the subscales of the Rushton Moral Resilience Scale, specifically moral adversity coping (β, -0.156; 95% CI, -1.241 to -0.039) and relational integrity (β, -0.245; 95% CI, -1.453 to -0.388), which are significant predictors of STS. Additionally, good sleep quality (β, -.396; 95% CI, -14.948 to -7.117) and seeking psychological counselling because of work difficulties (β, .107; 95% CI, 0.237-9.624) emerged as significant predictors of STS among ICU nurses, with the model's explanation of the variance in STS increasing to 45.5%, △R2 = .167, F = 16.482 (p < .001). This study found that ICU nurses have moderate levels of moral resilience and STS, which are negatively correlated. This suggests that improving the moral resilience of ICU nurses may help reduce their STS levels. The study revealed that ICU nurses' moral resilience and secondary traumatic stress levels were at a moderate level, indicative of the need to take measures to enhance their moral resilience and reduce their secondary traumatic stress, as their presence not only affects the health of ICU nurses but also diminishes the quality of care and increases turnover rates.