I am not sure I understand what you mean by: "Certainly I dont want the model workspace to do this job but diriectly in the model level in explorer.I just found some solution using clipboard,but was not successful.". Please elaborate.
One solution that I can see from my current understanding of your issue is:
rt = sfroot; m = rt.find('-isa','Simulink.BlockDiagram','-and','Name','%modelname'); constants = m.find('-isa', 'Stateflow.Data','scope','constant'); mdlWkspc = get_param('%modelname','modelworkspace') assignin(mdlWkspc,constants.Name, %constantValue)
Please provide details of why this solution does not meet your needs.