Abstract: Van Lookeren studied the steam flooding frontier prediction model when the pseudo mobility ratio was zero，and
proposed the steam injection parameters were optimal，while the shape factor got its maximum value.But in actual reservoirs ，the pseudo mobility ratio was usually not zero but greater because of higher oil viscosity or lower injection rate.In this case，the optimal method of steam injection parameters was limited.In this paper，the steam flooding frontier prediction model considering pseudo mobility ratio is studied，the charts among shape factor，pseudo mobility ratio and steam injection rate are drawn.It can be concluded from the charts that increasing steam injection rate can increase shape factor，so as to decrease the pseudo mobility ratio，reduce steam override and increase sweep efficiency.For steam injection rate was limited by pressure，the correlation among them was studied.Through the correlation and frontier model，the optimal method of steam injection parameters was modified.

Key words: steam flooding frontier, pseudo mobility ratio, shape factor, steam injection rate, parameters optimization