The invention discloses an online pH detection system for a direct drinking machine. The online pH detection system comprises a pH detection module, a temperature detection module and a correction module, wherein the pH detection module and the temperature detection module are sequentially arranged between a water way inlet and a water way outlet of the direct drinking machine, the pH detection module is used for detecting the initial pH value of a water way of the direct drinking machine, the temperature detection module is used for detecting the temperature value of the water way of the direct drinking machine, the input end of the correction module is connected with the pH detection module and the temperature detection module, and the correction module is used for obtaining pH detection values according to the initial pH value and the temperature value. The pH values detected and uploaded by the front-end device are recorded in real time, instant message monitoring and alarming are carried out, pH value historical data analysis and trend analysis of the device can be made, and a user can know the water quality condition of the device through mobile Internet.