Abstract:Collected the birch barks,branches and leaves of plant samples in four habitats of sunny slope,shady slope,forest edge and isolated trees in different diameters of Betula platyphylla in Huanglong mountain forest farm of northern Shaanxi Province in loess plateau,to illustrate the variation of betulin and betulinic contents.The samples extracted by ultrasonic assisted extraction,and used an accurate HPLC method to detect betulin and betulinic acid contents in different habitats and different diameters.The result indicated that there was a great variation between different habitats,and it was showed concretely as follows: (1) The contents of betulin and betulinic acid in barks and the contents of betulinic acid in branches ranged from high to low as shady slope,isolated trees,forest edge and sunny slope.The contents of betulin and betulinic acid in leaves and the contents of betulin in branches ranged from high to low as shady slope,forest edge,isolated trees and sunny slope.(2) The contents of betulin and betulinic acid in various organs of birch from high to low as bark,branch,leaf.(3) The betulin and betulinic acid contents of the different organs in different habitats increased first and then decreased with the increasing DBH of the trees,and the top value was observed in the DBH of 10.1-20 cm.The research suggested that shady habitat conducive to the accumulation of betulin and betulinic acid in various organs;the content of betulin in different organs of B.platyphylla is higher and the content of betulinic acid in different organs is lower,and betulin as raw material to prepare betulinic acid is an effective way to solve the betulinic acid in low levels of natural plants and difficult to extract;Attentions should be pay to grasp the opportunity of the organs of B.platyphylla,it is better to collect when the DBH of birch grows to 10.1-20 cm.