DAG-MAP is an FPGA technology mapping algorithm for delay optimization and the labeling phase is the algorithm’s kernel. This paper studied the labeling phase and presented an improved labeling method. It is shown through the experimental results on MCNC benchmarks that the improved method is more effective than the original method while the computation time is almost the same. DAG-MAP is an FPGA technology mapping algorithm for delay optimization and the labeling phase is the algorithm’s kernel. This paper studied the labeling phase and presented an improved labeling method. It is shown through the experimental results on MCNC benchmarks that the improved method is more effective than the original method while the computation time is almost the same.