Difference　resonator　is　a　kind　of　periodic　signal　detection　method,　but　its　phase　diagram　becomes　fuzzy　under　strong　noise　background.　In　order　to　get　its　clear　phase　diagram,　the　convergence　time　of　a　difference　resonator　was　calculated　with　its　mathematical　model,　and　the　relationship　between　the　convergence　time　and　the　resonator　parameter　β　was　derived.　Based　on　this　relationship,　its　clearer　phase　diagram　could　be　drawn　and　the　improved　principle　of　selecting　the　resonator　parameters　was　proposed.　The　advantages　of　the　proposed　method　were　validated　with　theoretical　analysis,　MATLAB　numerical　simulation　and　tests.