Abstract: Assuming the cycle T1 of sine wave of the sine electromagnetic wave pulse is equal to the central frequency of the isosceles wave of the isosceles trapezium electromagnetic wave pulse and both have same general pulse cycle T. Studying the axial energy's decaying property of the two waveforms on the same circular radiation antenna through the analytical and computer digital simulation, the results indicate:(1) In the slow decaying area of the isosceles trapezium electromagnetic wave pulse's propagation, when the rising time of isosceles trapezium waveform is less than one twentieth of the sine waveform's period, the axial energy's decaying property of isosceles trapezium electromagnetic wave pulse is better than that of sine electromagnetic wave pulse; (2) If k, the number of sine waveforms contained in one sine electromagnetic wave pulse, is far larger than 1, the sine electromagnetic wave pulse, no matter what different value of k, will have same decaying property.