Abstract: In order to observe the dynamic features of physiological functionof human body during the initial stage of space fligh and to study the mecha-nism of “space adaptation syndrom”,the heart rate,respiration,head and legbody surface temperatures and EEG were observed in 12 subjects during head-down 6°bed-rest.All the indices were recorded in a physiological data aquis-sition and processing system for out bed-rest laboratory.Analysis items includethe trend of heart rate,body temperatures,respiration and EEG during 24hbed-rest.R-R spectrum and EEG power spectrum.The results showed that some important physiological functions such asheart rate,respiration and EEG,were still remained circadian during head-down bed-rest,But some extent disorders were appeared,i.e.(1)The twohumps of heart rate rhythm which appear in normal condition were disappearedor indistinct,and the phase of heart rate rhythm was shift.(2)The circadianrhythm of body temprature was changed.The rhythem in head surface tempe-rature disappeared and the surface temperature in leg increased significantlyduring the intinial several hours,after then decreased,and the fluctuationwas remarkable.(3)The power in α band decreased and the power in δand θ band increased during bed-rest.The biorhythmic analysis indicated adecrease of circadian rhythm stability and showed a phase shifting.The resu-lts of R-R spectrum and and EEG power spectrum showed that the regulationof heart and brain and cerebral cortical activities were changed during 24hbedrest.