Due to the influence of outdoor climate and indoor human activities, the moisture accumulation of building enclosure structure will lead to the growth of mould on the interior surface of the wall, damage the building structure and endanger human health. Taking an office building in Dachangshan Island of Dalian, a cold area in North China, as an example, the outdoor relative humidity is high, and the temperature difference between indoor and outdoor is large during the heating period, which is easy to cause the increase of moisture content of the enclosure structure and the growth of mould. This study focuses on the influence of the heat and moisture transfer characteristics of the office building wall on the growth process of mould on the interior surface of the building. The dominant fungi of indoor air and wall surface were Penicillium and Cladosporium. WUFI software was used to simulate the heat and moisture transfer and the growth process of mould on the inner surface of the wall. The results show that the relative humidity of the air micro layer on the inner wall surface of the office building reaches more than 80% at the beginning of heating period in November every year, the mould hypha grows significantly in December and brings pollution risk. Finally, the relative humidity drops below 70% after the heating period is over in April, and the mould stops growing. The main reason for this phenomenon is that the condensation interface in the wall structure during the heating period leads to the accumulation of water in the wall, which is then transmitted to the wall surface through the wall pores, thus increasing the moisture content. This method provides a r eliable way for the numerical simulation of indoor mould growth risk.