An experiment was conducted by the methods of path analysis and competition index based on biomass,to study the impact of different planting density of Catalpa ovata seedling above-ground and below-ground competition to general competition.The result showed that there were close relationship among above-ground biomass,below-ground biomass and total biomass,with the density increased the biomass of root,shoot and leaves decreased and the ratio value of above-ground biomass with below-ground biomass was lower than 1.Above-ground competition was obviously larger than below-ground competition under the same density.The direct effect of above-ground competition on general-competition was from 0.449 3 to 0.973 1,which was obviously larger than below-ground competition on general-competition (0.275 6~0.773 2).Shoot and leaves of C.ovata seedling competition play an important role in general-competition.