Objective To analyze the clinical courses and outcomes of COVID-19 cases and the influencing factors in Guangdong province and provide basis for the formulation or adjustment of medical care and epidemic control strategy for COVID-19. Methods We collected demographic data, medical histories, clinical courses and outcomes of 1 350 COVID-19 patients reported in Guangdong as of 4 March 2020 via epidemiological investigation and process tracking. Disease severity and clinical course characteristics of the patients and influencing factors of severe illness were analyzed in our study. Results Among 1 350 cases of COVID-19 cases in Guangdong, 72 (5.3%) and 1049 (77.7%) were mild and ordinary cases, 164 (12.1%) were severe cases, 58 (4.3%) were critical cases and 7 (0.5%) were fatal. The median duration of illness were 23 days ( P 25 - P 75 : 18-31 days) and the median length of hospitalization were 20 days ( P 25 - P 75 : 15-27 days). For severe cases, the median time of showing severe manifestations was on the 12th day after onset ( P 25 - P 75 : 9th to 15th days), and the median time of severe manifestation lasted for 8 days P 25 - P 75 : 4-14 days). Among 1 066 discharged/fetal cases, 36.4% (36/99) and 1.0% (1/99) of the mild cases developed to ordinary cases and severe cases respectively after admission; and 5.2% (50/968) and 0.6% (6/968) of the ordinary cases developed to severe cases, and critical cases respectively after admission. In severe cases, 11.4% developed to critical cases (10/88). The influencing factors for severe illness or worse included male (a HR =1.87, 95% CI : 1.43-2.46), older age (a HR =1.67, 95% CI : 1.51-1.85), seeking medical care on day 2-3 after onset (a HR =1.73, 95% CI : 1.20-2.50) pre-existing diabetes (a HR =1.75, 95% CI : 1.12-2.73) and hypertension (a HR =1.49, 95% CI : 1.06-2.09). Conclusions The course of illness and length of hospitalization of COVID-19 cases were generally long and associated with severity of disease clinical outcomes. The severe cases were mainly occurred in populations at high risk. In the epidemic period, classified management of COVID-19 cases should be promoted according to needs for control and prevention of isolation and treatment for the purpose of rational allocation of medical resources.