To improve the economy, larger bypass ratio has been adopted in the turbofan engine design, leading to a larger fan high, larger speed gap between HP and LP turbines, the meridian geometry of the engine will be excurvature at a high degree, which brings problem for the design of LP turbines, transition section between HP and LP turbines. In this paper, in accordance with such characteristics, adopted two ways to redesign a better turbine, and two modified turbines was simulated to study how to control flow separation of LP turbines and the transition section, improve its aerodynamic performance. The results indicated that adopted the two ways to improve the performance is effectual, but the forward-swept and wide-chord blade technology is more effectual.