Steam-assisted gravity drainage ( SAGD) process has many advantages over other thermal recovery methods for bitu-men recovery. The current models used for productivity prediction of the SAGD process have been found not adequate for field application since the effects of steam nonconformance along the well were not considered. In this study, dedicated laboratory experiments were conducted to investigate the sectional recovery along the horizontal well during simulated SAGD process. A new mathematical model considering non-uniform steam distribution was established based on the experimental results and com-bining the Darcy's law and heat transfer as well as mass balance models in the SAGD process. The results indicate that the real 3D SAGD recovery process along the horizontal well is more complex than that described in a single 2D vertical profile, and the newly proposed model is more accurate in productivity prediction than the previous models. The previous descriptions of the steam distribution in a 2D profile (i. e. the rising steam chamber, the lateral expansion of the steam chamber when it reaches cap-rock, and the declining steam chamber when it reaches the boundary) are not applicable for the whole horizontal well sec-tion. Moreover, steam quality is an important factor that can influence the steam distribution along the horizontal well.