In the processes of steam flooding in heavy oil reservoirs，the steam overlay and channeling often occur，which leads to small sweep efficiency of steam and low recovery efficiency of oil. Aiming at these problems，three experiments were conducted with a three-dimension displacement system，which included steam flooding，steam flooding converting to urea assisted steam flooding and steam flooding converting to urea-foam assisted steam flooding. The results show that the effect of the conventional steam flooding is not satisfactory；however，that of steam flooding converting to urea assisted or to urea-foam assisted steam flooding is better. After the conversion points of these two experiments，the instantaneous oil steam ratio was increased by 0.24 and 0.27 respectively；the recovery efficiency was improved by 9.56% and 16.29% respectively；the pressure difference between inlet and outlet increased by 0.18 and 0.33 MPa respectively and the instantaneous water cut decreased by 15.77% and 36.80% respectively. Variation of three-dimension temperature fields shows that the urea assisted steam flooding can expand the steam swept area but the effect is not obvious，and the urea-foam assisted steam flooding can control the steam overlay and channeling effectively and improve the sweep efficiency of the steam and produced degree of the oil. Comprehensive comparison of the above indexes indicates that the effect of urea-foam assisted steam flooding is the best.