The invention discloses a synchronous polarization phase shift focus measurement 
system based on a Linnik type interference 
microscope. The 
system comprises a 
white light source, a collimating mirror,a first quarter wave plate, a 
laser light source, a Kohler illumination 
system, a polarizing 
prism, a transflective mirror, a cubic 
beam splitting prism, two 
microscope objectives, a 
reference plane,a second quarter wave plate, an analyzer, a focusing lens, a 
beam splitting prism, an x-direction 
line array CCD and a y-direction 
line array CCD. The 
white light source generates 
white light, and plane polarized light is formed by means of collimation, polarization and the like. After being split by the cubic 
beam splitting prism, the light irradiates the 
reference plane and a tested sample through two 
microscope objectives. The return light is split by the beam splitting prism, and then irradiates the x-direction 
line array CCD and the y-direction line array CCD to generate an interference fringe image. Focus measurement is realized according to the defocus aberration change of the image. 
Laser is uniformly emitted by the Kohler illumination system, and is reflected by the polarizingprism and the like. The sample is directly written through the cubic beam splitting prism and the like. The system provided by the invention has the advantages of fast 
data processing and real-time focusing, and can acquire the position and shape information of the tested sample.