The correlation between pyrolysis conditions and fuel production has been extensively studied. Terahertz parameters, instead of thermal kinetic parameters, were investigated to reveal such interior correlation in this work. Different ventilating rate (V), heating rate (beta) and final temperature (T) were controlled in several pyrolysis experiments of oil shale two prepare semicoke with varied amount of oil content, respectively. It was observed that V = 0.6 L/min, = 15 degrees C/min and T = 550 degrees C were the expected conditions to produce fuel. The critical points in terahertz parameter corresponded well with that in oil yield. Intervals where increasing V,beta and T contributed to oil yield best can be determined by comparing the trend of absorption index at 0.4, 0.6, 0.8, 1.0 THz. Therefore terahertz parameter of semicoke may characterize the organic matter in semicoke that may convert to additional fuel and terahertz method can be applied to optimize pyrolysis efficiency. (C) 2017 Elsevier Ltd. All rights reserved.