Abstract: In order to calculate GMB=S_lx/S_y, the cross section of tree crown bottom was regarded as a rhomb whese diagonal lines were formed by the length (crown length) from east to west and from north to south, and as a circle with a longer diameter in the two crown length to calculate the rhomb area(S_lx) treating as real crown acre and the circle area(S_y) treating as potential or theoretical area With 12 centric sample plots of Picea schrenkiana var. tianshanica young plantation in 1987 and 1993, the GMB were calculated The results show that the tree crowns in accord with the golden section(0.599 ≤ GMB ≤ 0.637) are symmetrric while those out of accord with the golden section(GMB < 0.599) are bias crowns And the results also show that the GMB can not only reveal the competition structure, but also can be taken for an index to use into thinning theories Therefore, the study on the golden section in the tree crown has both an important value and an applicable potentiality.