The study derives the time of each departure flight from apron to holding pad, in which flights are consecutively assigned in a congested airport, and calculates the fuel cost of each flight due to taxiing and waiting for departure. The study then explores the block-queuing conditions of departure flights to construct a block-queuing assignment model with various situations and decide whether a departure flight should wait at terminal apron or holding pad. Furthermore, the study formulates delay cost functions with respect to passengers, airlines, and airport operators. Finally, the study collects data on the schedule of departure/arrival flights and the delay of departure flights in the Taiwan Taoyuan International Airport to demonstrate the application of the model. The results show that the block-queuing assignment method reduces fuel cost significantly more than the consecutive assignment method. It may increase the fuel-saving efficiency, while reducing airport operators' cost due to an idle runway and passengers' cost caused by delay in the airport.