Abstract: The sample (0.400 0 g) of trimeric cyclopentadiene (TCPD) was dissolved in and made its volume to 5.0 mL with toluene which was used as sample solution for GC determination of its 4 isomers. TC-WAX capillary column was selected for GC separation, and the 4 isomers were effectively separated under the following conditions:1 column temperature was elevated from the initial value of 50℃ to 230℃ at a rate of 6℃·min^-1 and kept for 10 min at this temperature; and 2 separation-flowing ratio of 3 to 1 was taken. Hydrogen flame ionization detector was used in the detection. External standard method was adopted for quantification. Linear relationships between values of peak areas and mass concentrations of the 4 isomers were found in the same range of 5.00-100 g·L^-1, with detection limits (3S/N) in the range of 2.0-2.5 mg·L^-1. Recovery was tested by standard addition method, giving values of recovery ranged from 94.8% to 106%, and RSDs (n=10) of the measured value were all less than 2%.