The invention discloses an integral multi-parameter water quality on-line monitoring device which is provided with a residual chlorine-water temperature sensor, a turbidity sensor and a water level sensor, and signal lines thereof are respectively connected with a single-chip microcomputer; the device is characterized in that the single-chip microcomputer is also connected with a keyboard input circuit, an output display circuit, an EEROM memory, a sound-light alarm circuit and a communication circuit; the output display circuit displays the concentration value, the turbidity value, the waterlevel height valve and the temperature valve of the residual chlorine in a circulating way; when a parameter exceeds the alarm value, the sound-light alarm circuit gives off sound-light alarm signals; the invention also expresses a control method which mainly comprises the following steps: system initiation, data acquisition, data processing and display, comparison and alarm; data acquisition adopts weighted average, data processing adopts moving average; and finally the invention can support the simultaneous on-line detection of a plurality of parameters, has the advantages of low cost, simple structure, convenient installation and debugging and high precision, and is very applicable to the water quality detection of small rural water plants.