In this study, the detoxification potato plantlets plants of ‘Longshu No.3’ were cultivated under PEG4000(0, 2%, 4%, 6% and 8% PEG) and gradient saline stress (0, 25, 50, 100 and 200 mmol·L NaCl) respectively. The root growth and the ultrastructure of mesophyll cell were observed two weeks later. The physiological and biochemical indices were measured to provided the theoretical basis for screening salttolerant and droughtresistant potato germplasm. The results showed that: with the increase of external PEG4000 or NaCl concentration, (1) the total of root length, root volume and root number were decreased. With extension of time the decrease was obvious. This decline in salt stress obviously greater than that in drought stress, explained that roots were sensitive to salt stress; (2) potato plantlet cell wall obviously thickened and plasmolysis, plastoglobuli markedly increased, numerous vesicles, chloroplasts gradually damaged to a complete disorganization; (3) potato plantlet plants leaf proline content significantly increased, the activities of catalase (CAT) and superoxide dismutase (SOD) and malondialdehyde (MDA) content significantly increased, while chlorophyll content decreased. In conclusion, the PEG4000 simulated drought and salt stress could cause serious damage of plant chloroplast structure and chlorophyll content significantly decreased. The more stress and the more serious damage. Simultaneously, drought and salt stress also induced that potato plantlet leaf proline content and the activities of catalase (CAT) and superoxide dismutase (SOD) significantly increased and alleviated the drought and high salt stress injury.