Aiming at the cracking phenomenon of the thin shell mould in the expendable patt shell casting during the patt removing process, some systemic researches are presented. The influence of the patt removing method and temperature on the patt removing were investigated. The shell mould cracking mechanism was analyzed by using thermo-gravimetric analysis (TGA), and combining the temperature field and the volume change of the expanded polystyrene (EPS) foam pattem being tested. The results indicated that the shell mould was not easily cracked when the patt removing process was carried out with the face being heated little by little because of the shell slowly shrinking with dehydration and shell strength gradually increasing. The shell mould was soon destroyed when it was set directly into the fumace at above 400 ℃ because of the thin shell mould rapidly shrinking and the foam patt hindering. However, the shell mould had no cracking when it had been preheated for a long time even if the face temperature was above 400 ℃ and the shell was put into the face directly. Moreover, when the shell mould was directly set into the face at lower temperatures, 250 to 300 ℃, the shell would shrink slowly and the foam patt would stay at the maximum expansion stage temperature of 100 to 110 ℃ for a long time; and the shell mould would experience an expansion force from the foam patt for a long time. The expansion force is related to the patt removing temperature, holding time, foam patt thickness and density. Therefore, the foam patt with higher density could make the shell crack.