A monitoring, forecasting and alarm system of the bottom and hearth of a blast furnace belongs to the longevity technical field of blast furnaces. The system comprises online monitoring and forecasting hardware and software processing modules; the online monitoring and forecasting hardware consists of a thermocouple and a cooling system which are laid at the furnace hearth and the furnace bottom, and a database of the blast furnace production process is connected by the Ethernet; the software processing modules comprise a data acquisition module, a data validity judgment module, a temperature field computation module, an improved genetic algorithm module, a B-P neural network module, a database, an isotherm, an erosion and thickening image display module, a 3D imaging module, a heat flow monitoring and alarm module and a historical data query module; and the software processing modules are operated on an industrial control computer. The monitoring, forecasting and alarm system has the advantages of low investment, reliability and visualization. The system provides an objective and quantized basis for the erosion and thickening erosion condition of the furnace hearth and the furnace bottom in the blast furnace ironmaking process, and helps a blast furnace operator timely know the condition of the furnace hearth and the furnace bottom and take effective furnace protection measures so as to prolong the service life of the blast furnace.