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LThe effect of thermostress shock on the membrane permeability and protein secondary structure of the desert moss Tortula desertorum was investigated by electron paramagnetic resonance and in situ Fourier transform infrared microspectroscopy. The results of spin label showed that plasma membrane permeability was changed significantly among different aging tissues and increased by aging in control level. However, after treated at 45 degrees C for I h, membrane permeability was promoted by contraries to aging. The changes in secondary leaves and protonema were most pronounced, increased 4 doubles after treatment. The protein secondary structure of T. desertorum, was affected by thermostress through analyzing the spectra of FTIR using second-derivative, Fourier self-deconvolution and curve-fitting. The components of protein secondary structure were obviously different among various aging leaves, indicating that types of proteins changed in leaves. The content of a-helix was increased 40% and 16% in secondary leaves and protonema respectively after thermostress than that of initial. Aging leaves were little changes in protein secondary structure, it showed there was no drainatically damage to them. The results of membrane permeability and protein secondary structure proved the proteins stability were negative correlation with changes of’ permeability, indicating types and content of proteins might be one of the most important reasons causing aging leaf difference in response to high temperatures.