Merits and demerits of the directed relation graph (DRG) method are analyzed. On the basis of these analyses, a flux projection tree (FPT) method for mechanism reduction is proposed. A tree-type structure is constructed in FPT based on the contribution of each species to the global flux; that is, the importance of each species is quantified by normalized projection of its participation flux vector upon the total species flux vector. Because a tree-type structure is simpler than a graph-type structure, FPT tends to be more efficient than DRG and path flux analysis (PFA) in computation. Additionally, the significance of each species in a mechanism is estimated on the basis of its contribution to the global species flux, instead of its contribution to the flux of a single species in a pre-chosen important species set, as in DRG and PFA. Thus, a reduced model obtained by FPT is more accurate in most cases. Detailed mechanisms for oxidation of ethylene, n-heptane, and PRF50 were reduced with FPT, and the reliability of the resulting skeletal mechanisms is comparable or even better than that of the skeletal mechanisms obtained by DRG or PFA with similar size. Because of its high efficiency, FPT can be used as the first-step reduction method or on-the-fly mechanism reduction approach in numerical simulations of reaction flow.