The azimuth average sequence of δ¹³C in tree rings of two Cryptomeria fortunei Hooibrenk ex Otto et Dietr disks(named CF-1, CF-3,respectively) and eight Pinus massoniana Lamb disks(named PM-1-PM-4, PM-7-PM-10,respectively), as well as the average orientation annual series of δ¹³C in tree rings of Cryptomeria fortunei, were investigated using harmonic analysis. Data related to Cryptomeria fortunei and Pinus massoniana were collected from Tianmu Mountain, Zhejiang Province and Purple Mountain of Nanjing, Jiangsu Province, respectively. The analysis showed the azimuth variations of δ¹³C in tree-rings had very strong harmonic characteristics. The variance contribution of the first and second harmonic components as a percentage of the total variance of the original sequence were mostly above 70%, including CF-1 and PM-9 which reached 93% and 96.5%, respectively, the two exceptions were PM-8 and PM-10. The correlation coefficients were greater than 0.8 (P ＜ 0.05) between the first and the second (or the third) harmonic fitting sequence, and the original sequence. The two harmonic fitting sequences were relatively high, both above 75%, and exhibited a good fit to the data. The azimuth variations of δ¹³C in tree rings could be well explained by two harmonic cycles of 2 π and π (PM-1 and PM-7 were 2 π/3). The initial phase values of the first and the second harmonics had clear differences. This indicates that the doubling of the harmonic amplitude peak in different trees was present in different azimuth regions:the maximum of the azimuth variations of δ¹³C in tree rings with 2π and π harmonic cycles were in different regions. When the results of the two harmonic cycles were superimposed, the orientation of the maximum δ¹³C in tree rings became complex. Harmonic analysis of the average annual sequences of δ¹³C in different azimuths of C. fortunei showed that the extremes have obvious inter-annual drift. The azimuths of the δ¹³C maximum changed with slope of tree growth. In most years, the azimuth of the δ¹³C maximum transferred 45°, but when the main and secondary maximums were superimposed, it became 90°. The change in the direction and magnitude of the δ¹³C maximums are consistent with the slope changes in the growth of the two trees.