The invention relates to a refractory brick inside quality online detection device comprising a hardware system and a software system. The refractory brick inside quality online detection device is characterized in that the hardware system adopts a modular structure comprising a main processing module, a voice acquisition module, a PC serial communication module, an auxiliary external module and a knock control module; a main processing chip of the DSP main processing module is a TMS320V5509A chip which is used for managing an external memory space through an internally and externally arranged external memory interface, the external memory space is divided into CE0-CE3, and each space is provided with a chip selection use signal/CEn. The software system provides a method for detecting and diagnosing inside defects of a refractory brick by utilizing a refractory brick knock acoustical signal and develops corresponding software. The invention solves the problem that the refractory brick inside quality detection device is outmoded, ensures that a refractory brick inside defect detection device is stable and rapid to run, simple to operate and complete in function and can completely meet the requirement of refractory brick inside quality online detection, thereby being applied to refractory brick production plants for improving the production quality and the efficiency.