This paper aims to develop an advanced three-shaft turbofan engine with ultrahigh bypass ratio (BPR) for entry-into-service (EIS)2050. The boundary approaching method is utilized to obtain the optimal engine for a series of engines with different fan diameters. Furthermore, the flight mission analysis was carried out to fully consider the engine performance and weight penalty. The optimum engine employs a 3.26 m fan diameter with ultrahigh BPR reaching 21.39. The corresponding specific fuel consumption (SFC) is 11.42 (g/s)/kN, which is 3.88% lower than the 2.95 m fan diameter engine. However, the weight penalty has offset part of the benefits, and the block fuel reduction is 2.5%. Sensitivity analysis results reveal that the low-pressure turbine (LPT) efficiency plays a dominant role in engine performance. Afterwards, the effects of variable geometry are investigated including the blow-off valve (BOV), variable inlet guide vane (VIGV), and bypass variable area nozzle (VAN). Results show that combining the three measures would boost engine performance and save fuel. The designed schedule for the combination of VIGV, BOV, and VAN has generated a reduction in block fuel, NOx, CO2, and H2O reaching 3.36%, 5.55%, 2.47%, and 2.53%, respectively.