This paper have built a dynamic mathematical model for simulating the coupled heat and moisture transfer and validated it by comparing with typical case.On the basis of the transient distribution of the temperature and the relative humidity,the paper is inclined to propose the concepts of humidity threshold value for mould germination risk,and heat-humidity critical lineto evaluate mould germination risk.And it studied indoor temperature-humidity threshold values for mould germination risk on the typical hygroscopic walls (red brick wall and aerated concrete wall) in some south cities of China...