The pollution flashover problem of composite pillar insulators, as one of the major faults in substations, can be effectively improved by optimizing the shed parameters. This paper proposes a shed parameter optimization method based on the physical model of composite post insulators. Firstly, through simulation calculation we studied the effects of the extension of the large shed overhang P1 and the shed spacing s on the electric field distribution. With the optimization target of reducing the average electric field Eav along the skirt or the non-uniformity coefficient f along the skirt, the parameter optimization range was obtained as 70 mm≤P1≤90 mm and 72 mm≤s≤92 mm, providing a parameter range for subsequent shed parameter optimization experiments. Then, using physical models of composite post insulator as test samples, artificial pollution tests were carried out to observe the flashover voltage, ultraviolet discharge photon number, and arc development path of the test samples. The optimal(maximum flashover voltage) shed parameters were obtained as P1=90 mm and s=72 mm, and the pollution flashover voltage of the optimized sample was increased by 18%. Finally, the simulation and experimental results were comprehensively analyzed, and the priority of simulation optimization criteria was proposed. The average electric field Eav along the skirt mainly affects the flashover voltage U50%, and the smaller the Eav of the test sample, the larger the U50% and the weaker the bridging and crossing phenomena of the arc; the non-uniform coefficient f along the skirt mainly affects the ultraviolet discharge photon number, and the smaller the f of the test sample, the fewer the ultraviolet discharge photon number. In the optimization strategy based on electric field simulation, the priority of Eav should be higher than that of f, and the surface creepage coefficient should be close to 3.5-4.0.