The invention discloses an online bridge monitoring system based on an MDG-SC algorithm. The online bridge monitoring system comprises a signal collection part composed of sensors installed on a bridge, a signal processing and network transmission part, and a cloud service and data processing part, wherein the signal processing and network transmission part communicates with the cloud service anddata processing part through a Lora wireless sensor network adopting a mobile sink strategy, the moving speed of the mobile sink MS is optimized by the MDG-SC algorithm, that is, when a sub-sink S covering the location of the mobile sink MS is 1, the moving speed of the mobile sink MS is a data rate SP1 of the sub-sink S; when the sub-sink S covering the location of the mobile sink MS is greater than 1, the moving speed of the mobile sink MS is the lowest data rate SP2 in all sub-sinks S; and when the sub-sink S covering the location of the mobile sink MS is 0, the moving speed of the mobile sink MS is SP3, and SP3 is greater than SP1 and SP2.