In this paper, an analytical solution is presented for stress intensity factor of a solid circular cylinder with an edge crack subjected to transient hygrothermal loading on the lateral surface. It is assumed that the coupled diffusion problem of temperature and moisture in the cylinder over a short time can be analyzed by neglecting the hygrothermal disturbance near the crack tip. The associated plane-strain hygrothermal stress problem is solved by the use of Tweed and Rooke's solution for a pure elastic problem in a circular cylinder with the same crack. Numerical calculations are carried out for the stress intensity factor at the crack tip in the circular cylinder made of T300/5208(graphite/epoxy) composite material. The effect of crack length and coupling of temperature and moisture fields on the stress intensity factor are quantitatively estimated under various thermal and hygrometric loading conditions.