The invention relates to a real-time observation single-beam dual-mode parameter adjustable Z scanning device and measurement method. The device mainly comprises a parameter modulation part, a data acquisition part and an observation part, wherein in the parameter modulation part, after passing through an adjustable attenuator and an acoustooptical adjustor, laser is transformed into a laser beamwith adjustable power pulse and is focalized onto the surface of a sample by lens; in the data acquisition part, emergent light on the back surface of the sample is divided into two beams by a dispersion prism, one beam of light directly enters a detector thus the nonlinear absorption of material is acquired, and the other beam of light enters the other detector by a small aperture of which the center is coaxial with an optical axis thus the nonlinear refraction of the material is acquired; and in the observation part, a cold light source illumination device is additionally arranged on the light path of the device so that the change of points of action can be observed in real time in experiments. The invention is easy to realize, and can acquire the nonlinear absorption rate and the nonlinear refraction rate of materials in different conditions.