In order to study the effect of polymer microsphere profile control and flooding on produced fluid and deepen the understanding of the profile control and flooding mechanism of polymer microsphere, the produced fluid in typical blocks of major reservoirs such as ultra-low permeablity, super-low permeablity and low permeablity in Changqing oil field were analyzed and studied. After using gravity separation and centrifugal separation methods to obtain crude oil and produced water, the changes in the composition of crude oil group, K⁺, Na⁺, Ca²⁺, Mg²⁺, ions, and water content in the produced water before and after profile control were analyzed, and the variation patterns were summarized. The results show that after injecting polymer microspheres into each typical block, the saturated alkane content in the crude oil decreases, the non-hydrocarbon content increases, the water content significantly decreases, and the salinity of the produced water increases. Through the above research, it has been further clarified that polymer microspheres mainly play a "blocking" role in reservoirs, and residual oil is utilized by expanding the swept volume of injected water, providing a theoretical basis for the production increase of Changqing Oilfield through profile control and flooding.