The worldwide COVID-19 outbreak caused by 2019-nCoV infection has been declared as a public health emergency of international concern by the World Health Organization (WHO). COVID-19 patients usually present with respiratory symptoms, while severe cases could also have extrapulmonary organ damages. The immune system is essential in defending against viral infection. However, clinical features as well as pathological findings of COVID-19 suggest that 2019-nCoV infection might cause immune deficiency. It has been revealed that immune imbalance and hyper-inflammatory state in COVID-19 patients are closely associated with disease progression and poor outcomes. This review provided an update on immune responses in 2019-nCoV-infected patients including innate immunity, adaptive immunity and cytokine storm, aiming to elucidate the role of immune system in the pathogenesis of COVID-19 and provide reference for clinical prevention and treatment of COVID-19.