The invention belongs to the technical field of petroleum reservoir exploitation, and in particular relates to an experimental method for testing the slow expansion performance in a polymer microsphere rock core. The method comprises the following steps: 1, making an artificial rock core: adopting a quartz sand epoxy resin bonding method to make the artificial homogeneous rock core; 2, pumping out the saturated water of the rock core: measuring the actual outline dimension of the rock core, calculating the overall volume of the rock core, weighing dry weight, pumping out the saturated water, weighing wet weight, and calculating the volume of the saturated water and the porosity; 3, calculating the water permeability of the rock core: establishing a relation curve of injection pressure difference and injection speed, and calculating the water permeability; 4, testing the slow expansion effect of polymer microspheres; 5, evaluating the slow expansion capacity of the polymer microspheres: finding out that the injection speed 0.3mL/min or 0.5mL/min corresponds to the injection pressure difference delta P0 on the water driving relation curve of injection pressure difference and injection speed established in the step 3, and calculating microsphere blocking rates at different moments.