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This paper determined the delta 13C annual series of three Cryptomeria fortunei tree rings at West Tianmu Mountain, and analyzed their similarities and differences. In the period of 1837 to approximately 1982, the correlations among the three delta 13C series were significant, with r12 = 0.47, r13 = 0.65 and r23 = 0.52 (P < 0.001, n = 146), respectively. After removing the high-frequencies from the original delta 13C series by using polynomial function model, a significant correlation was observed among three low-frequencies, with the correlation coefficient varied from 0. 95 to 0.998. A significant correlation was also observed between original low-frequencies and simulated high-frequencies, with the correlation coefficient being 0.79 to approximately 0.84. The three delta 13C annual series had similar high-frequency and low-frequency variations. High-frequency variation recorded similar climate variation information, while low-frequency reflected the information of atmospheric CO2 changes. It was the common case for different individuals of trees that in the three delta 13C annual series, climatic factors caused high-frequency change, while atmospheric CO2 concentration caused low-frequency variation. The differences among the three delta 13C annual series were mainly caused by the local environmental conditions at the growth sites of trees, while the individual difference among the three delta 13C series caused by local environmental conditions had very small effects on the changes of the three delta 13C series. It could be concluded that the differences among the three delta 13C series did not affect the suitability of using tree ring's delta 13C annual series as the indirect evidence in climatic variation study, and the reliability and coherence of reconstructing historical climate changes.