Abstract: High power pulsed fiber lasers are attractive for light detection and ranging (lidar) systems. However, the amplified spontaneous emission (ASE) noise of the high power pulsed fiber laser degrades the system performance. A method to measure the ASE noise inherited in the high power pulsed laser is proposed. Using this new method, the high power laser is attenuated firstly, and then the relative energies of the ASE noise and the laser pulse are measured and calculated separately in time domain. The attenuated ASE noise profiles as well as the ratios of the ASE noise energy to the laser pulse energy are presented at different pump conditions.