The invention belongs to the technical field of temperature detection, and discloses a blast furnace temperature online detection system, which comprises a temperature acquisition module, a signal conversion module, a data integration module, a data preprocessing module, a wireless transmission module, a remote monitoring module and a main control module, the master control module is used for processing and analyzing the collected data and carrying out coordinated control on the operation of each controlled module. According to the invention, the temperature acquisition module is used for detecting and acquiring the temperature in the furnace by a plurality of groups of temperature acquisition sensors mounted at different depth levels of the blast furnace body, and monitoring points are arranged at different positions in the furnace body, so that the accuracy and real-time performance of temperature acquisition can be effectively improved, and the detection process is continuous and reliable; by arranging the whole group of temperature detection sensors at the same position in the furnace body, data is more multidimensional and complex, the information amount is larger, the furnace temperature of the blast furnace can be continuously detected on line, and the real-time performance and accuracy of furnace temperature detection can be ensured.