Abstract: Radical evolution during maple lignin pyrolysis is monitored by the electron paramagnetic resonance spectroscopy（EPR）.Results showed that maple lignin pyrolysis radicals can be divided into three stages:the radical initiation stage below 450 ℃ in which the yield of liquid reaches the highest; the radical propagation stage between 450 ℃ and 550 ℃ in which the radical concentration increases sharply to 276.99×10¹⁷ spin/g at 550 ℃；the radical stabilization stage above 600 ℃. Furthermore, coupling change trend between temperature, hydrogen/carbon ratio,graphitization degree and radical concentration are separately well described by constructing regression equations,which provided a new idea to reveal the microscopic pyrolysis mechanism of lignin.