Using Zero-span tensile test technique, measurements of the longitudinal tensile strength of tracheids of brown-rotted Chinese fir were obtained in the present work. The results showed that the longitudinal tensile strength of tracheids reduced with the increase of exposure time. The absolute value of reduced tensile strength was not remarkable because of low degradation efficiency. The FTIR spectroscopy results shows that brown-rot fungus did degraded the cellulose and hemicellulose of Chinese fir, explaining the reduction of tensile strength of tracheids. The intensities of the characteristic aromatic lignin peak at 1512 cm-1 was not increased but decreased, which was very strange, hinting the reason of that is not clearly illustrate by the FTIR spectra only.