This paper presents a hardware Trojan classification method that performs a static analysis in gate-level netlist. Based on the controllability and observability characteristics extracted in a circuit, the nets are clustered into two groups with the k-means method. Then inter-cluster distance is measured and taken as the major feature for Trojan identification. By combined with three other features in terms of circuit scale statistic number, a complementary representation of Trojan circuits is constructed. Finally, a support vector machine classifier is trained to distinguish the Trojan circuits from genuine circuits. Experimental results on Trust-HUB benchmarks demonstrate that our method can achieve up to 100% true positive rate.