The utility model provides an online monitoring system for a high-altitude tundra power transmission line iron tower base. The system comprises a foundation base monitoring device, a pole tower monitoring device, a state monitoring agency device and an online monitoring and early warning master station for the power transmission line iron tower foundation base, wherein the foundation base monitoring device collects foundation base monitoring parameters of power transmission lines; the pole tower monitoring device collects pole tower monitoring parameters of an iron tower; the state monitoring agency device obtains the foundation base monitoring parameters through a WIFI mode, obtains the pole tower monitoring parameters through the WIFI mode and sends the obtained parameters to the online monitoring and early warning master station for the power transmission line iron tower foundation base through an OPGW mode; and the online monitoring and early warning master station for the power transmission line iron tower foundation base receives the foundation base monitoring parameters of the power transmission lines and the pole tower monitoring parameters of the pole tower through the OPGW mode and utilizes the obtained parameters for online monitoring of the high-altitude tundra power transmission line iron tower base. The online monitoring system realizes online monitoring of the high-altitude tundra power transmission line iron tower base.