A new fast bus protection algorithm based on inverse traveling wave energy entropy is proposed. Based on the S-transform of the backward traveling wave, the energy entropy is obtained and the protection criterion is analyzed. When the bus internal fault occurs, the energy entropy of the inverse wave s transform is the same, and the energy entropy of the fault line and the non fault line is different, and the energy entropy ratio criterion is established to identify the internal and external faults of the bus area. The simulation results show that the busbar protection method can be sensitive and reliable to identify the faults inside and outside the busbar area.