Oil source made up of constant pressure variable displacement pump, accumulator, and pipeline is widely used to provide stable pressure for electro-hydraulic control system in practical engineering. Based on the experiment, the relationship between pressure & volume of the accumulator at inlet of the valve and control precision is analyzed in detail, and coupling rules between the load variation and the pressure ripple of oil-source are obtained. Coupling rules can give reference for selecting pressure & volume of the accumulator according to the requirement of system control precision, which can further improve control precision and product quality by optimizing equipment parameters.