The cycloaddition reaction of dichlorocarbene with C~6~0 has been studied by using the semi-empirical method AM1. A reasonable mechanism of the reaction has been suggested. All the geometries of the stationary points on the reaction path way have been optimized by energy gradient technique and the transition states were characterized by vibration frequency analysis. The calculation results show that the reactions of dichlorocarbene with 6-6 or 6-5 bond of C~6~0 proceed via two steps: (1) Dichlorocarbene and C~6~0 form an intermediate complex with a pretty low barrier. (2) The intermediate complex forms the product C~6~0 CCl~2. After being corrected by zero-point energies the barriers are 10.59kJ·mol^-^1 of 6-6 cycloaddition and 131.56kJ·mol^-^1 of 6-5 cycloaddition reactions respectively. The reasons that dichorocarbene cycloaddition should take place across 6-6 bond rather than 6-5 bond of C~6~0 are explained from the reaction mechanism and kinetic factors.

Key words: FULLERENES, DICHLOROCARBENE, CYCLOADDITION REACTION, TRANSITION STATE THEORY, REACTION MECHANISM