Due to the lateral current transport in the mesa-structure GaN based LEDs，the resistance of the n-type material of the GaN and lower confinement layer is not negligible for large area and high applied current density applieations，which causes the current spreading nonuniformly along the lateral direction. With an optimized contact scheme to reduce the length for the lateral current transport，two different kinds of contact schemes of high-power GaN-based flip-chip LEDs (FCLEDs) are fabricated. It is shown that the forward voltage of this FCLED with interdigitated contact scheme is 3.35V at forward current 350mA，and exceeds that of FCLEDs with optimized ring-shaped interdigitated contact scheme by 0.15V. Although the light emitting area of FCLEDs with optimized ring-shaped interdigitated contact scheme is slightly smaller than that of FCLEDs with interdigitated contact scheme，it is found that the light output from the former is larger than that from the later at higher injection currents. Furthermore，the light output from the FCLEDs with optimized ring-shaped interdigitated contact scheme saturates slowly at higher injection currents as compared to the FCLEDs with interdigitated contact scheme，indicating that the saturation behavior of the FCLEDs with interdigitated contact scheme is more pronounced. It is confirmed that an optimized contact scheme，which leads to the more uniform current spreading，can decrease joule heat generated and considerably improve the electrical and optical characteristics of the FCLEDs.