Species diversity in a Pinus tabulaeformis mixed forest was studied using a 1 hectare plot on Huanglong Mountain. Different diversity indexes were used to analyze tree structure and undergrowth vegetation diversity. Results showed that diversity indexes stabilized at larger scales, with the shrub layer having the highest species diversity. The herb layer had the lowest species richness but more uniform distribution. The structure of the tree layer was linked to species diversity in the shrub and herb layers. Sampling scale is important when studying species diversity in this type of forest.