Hi Gopal,
It seems SAP Business One does not display the default value set for a parameter in Crystal Reports.
Have a look at this Enhancement Request on the Ideas Place:
https://ideas.sap.com/ct/ct_a_view_idea.bix?idea_id=%7B02DD1DF3-5D80-40ED-A803-B53891B46279%7D
Please do Vote Up if you think this is what you're looking for. More the number of votes, more the pressure on the Product Group to implement the functionality.
-Abhilash