The invention provides an imaging flow cytometer and relates to the field of optical instruments in biology and medical science. The problems that an existing imaging flow cytometer system is low in energy use rate in defocusing distance and speed measurement, complex in structure and high in cost are solved. A polarization optical system is introduced, richer biological information relative to samples to be measured can be acquired, and the imaging flow cytometer is mainly composed of a sample injection unit, a laser source, a speed measurement-focusing unit, an imaging unit and a central control unit. Meanwhile, based on the laser back scattering light spot imaging principle, the speed detection function of the samples to be measured and the automatic focusing function of the cytometer are finished. Through analysis of sequence signals of light signal intensity of the samples to be measured in different sensing positions of an array optical sensor and analysis of distribution of light signal intensity of the detection face of the sensor, the cell movement speed and the defocusing distance can be acquired at the same time, measurement is more accurate and visual, the energy use rate and the signal to noise ratio are higher by the adoption of a laser back scattering mode, and a single optical path detection structure is simpler.