Abstract: Fiber-reinforced resin matrix composite stiffened panels were put in water at 70 ℃ until the absorbing moisture reached a balance. The compression experiments were conducted for the common stiffened panels and the stiffened panels after absorbing moisture. The effects of hygrothermal environment on the buckling mode,buckling load,failure load and carrying capacity of the composite stiffened panel were studied. The results show that the failure modes of the two kinds of stiffened panels mainly contained the debonding and fracture of stiffener and the tearing of skin. Post-buckling progress still could be found after absorbing moisture of the stiffened panel. But its buckling load and failure load dropped by 8.2% and 19.2% after absorbing moisture.