Near-infrared spectroscopy (NIRS) technology and Mie theory are utilized for fundamental research on radiofrequency ablation of biological tissue. Firstly, NIRS is utilized to monitor rats undergoing radiofrequency ablation surgery in real time so as to explore the relationship between reduced scattering coefficient (μ^'_s) and the degree of thermally induced tissue coagulation. Then, Mie theory is utilized to analyze the morphological structure change of biological tissue so as to explore the basic mechanism of the change of optical parameters caused by thermally induced tissue coagulation. Results show that there is a close relationship between μ^'_s and the degree of thermally induced tissue coagulation; the degree of thermal coagulation can be obtained by the value of μ^'_s; when biological tissue thermally coagulates, the average equivalent scattering particle decreases, the particle density increases, and the anisotropy factor decreases.