The invention discloses an on-line leakage intelligent monitoring system based on multi-parameter monitoring and a monitoring method. The monitoring system includes a front-end leakage detection connecting device installed on a monitored device and a rear leakage monitoring device connected with the front-end leakage detection connecting device, the front-end leakage detection connecting device includes a plurality of leakage detection connecting pipes and a first connecting joint, a plurality of monitoring holes are arranged in the monitored device, each monitoring hole is connected with an inlet of one leakage detection connecting pipe, the rear leakage monitoring device includes a pressure monitoring device, a gas monitoring device, an acid-base value monitoring device, a data acquisition instrument, a master control device and a leakage alarm device, The monitoring method includes steps of monitoring project selection, alarm threshold setting, monitoring setting, and online leakage monitoring. The on-line leakage intelligent monitoring system is reasonable in design, simple in use, operation, and connection, and good in use effect, and can monitor the leakage conditions of the monitored device in real time online, the monitoring manner is flexible, the monitoring result is reliable, and the later query is simple.