A bench-scale fixed fluidized bed reactor was used to study the distribution and quality of productsderived from thermal cracking of VGO. Test results had shown that the space velocity has minor effect onthermal cracking reaction. The depth of thermal cracking reaction was mainly affected by the reaction temperature.At different reaction temperatures the form of free radicals thus initiated varied, resulting in different productdistribution. At low temperature C10= and C11= olefins dominated in thermally cracked gasoline products,whereas at higher temperature C6=C9= olefins dominated in thermally cracked gasoline products, amongwhich C6 and C7 olefins were mainly composed of 2M1C5= and 2E1C5=. Difference in olefin structure can leadto different reaction pathways of catalytic cycle.