This study aimed to assess current level of sodium and potassium intake and their associations with blood pressure (BP) using the 24-hour urinary data in a large sample of China. Data from participants aged 18 to 75 years were collected as the baseline survey of Action on Salt China in 2018. Of 5454 adults, 5353 completed 24-hour urine collection. The average sodium, potassium excretion, and sodium-to-potassium molar ratio were 4318.1±1814.1 mg/d (equivalent to 11.0±4.6 g/d of salt), 1573.7±627.1 mg/d, and 5.0±2.1, respectively. After adjusting for potential confounding factors and correcting for regression dilution, each 1000-mg increase in sodium excretion was associated with increased systolic BP (1.32 mm Hg [95% CI, 0.92–1.81]) and diastolic BP (0.34 mm Hg [95% CI, 0.09–0.60]). Each 1000-mg increase in potassium excretion was inversely associated with systolic BP (−3.19 mm Hg [95% CI, −4.38 to −2.20]) and diastolic BP (−1.56 mm Hg [95% CI, −2.29 to −0.90]). Each unit increase in sodium-to-potassium molar ratio was associated with an increase of systolic BP by 1.21 mm Hg (95% CI, 0.91–1.60) and diastolic BP by 0.44 mm Hg (95% CI, 0.24–0.64). The relationships between sodium and BP mostly increase with the rise of BP quantiles. Potassium shows the opposite trend. The current sodium intake in Chinese adults remains high and potassium intake is low. Sodium and sodium-to-potassium ratio were positively associated with BP, whereas potassium was inversely associated with BP. Registration— URL: https://tinyurl.com/vdr8rpr ; Unique identifier: ChiCTR1800017553. URL: https://tinyurl.com/w8c7x3w ; Unique identifier: ChiCTR1800016804. URL: https://tinyurl.com/s3ajldw ; Unique identifier: ChiCTR1800018119.