The invention discloses a method for realizing ultra-short single-pulse time-resolved pump probe by using a ladder window. Laser output by a laser unit is divided into pump light and probe light, thepump light is focused on a nonlinear sample through a lens to produce nonlinearity; the probe light probes change of the nonlinear sample induced by the pump light after being transmitted by the ladder window, and an image is received by a CCD; under the condition that the probe light undergoes different time delay, the change of the intensity of the probe light emitted from the sample reflects the condition of particle number population in the sample at different moments, so that the absorption cross section and the life of each energy level are determined. A measurement system working according to the method is very convenient in measurement, sample movement is not required, a time-resolved pump probe curve can be obtained only through one laser pulse, and the system is very simple as compared with traditional pump probe light paths. Time delay can be realized only through one delay ladder window instead of a high-accuracy movement platform in traditional light paths.