Abstract: The basic principle of neutron spectrum measured with time of flight method was introduced. The design of experimental device for the time of flight spectrum in the thermal column of the pulse reactor measurement was given, and the time spectrum measured result was shown at the same time. In the end, the measured thermal neutron spectrum of the thermal column resolved by the selfmade programs was offered. The experiment results prove that the measured spectrum is a little softer than Thermal Maxwellian theory spectrum, the neutron energy value corresponding with the measured spectrum peak point is about (24.8±7.2) meV.