To Pass Main Reports Parameter Field Value to Subreport (Crystal Reports)

Step-1 Right click on sub report container in main report, Select -> Edit Sub Report
Step-2 Create the parameter in sub report (if not exists)
Step-3 Return to Main report
Step-4 Right click on sub report container once again and select -> Change sub report links..
Step-5 Select the parameter field (defined in master report) from 'Container Report fields to link'--> Available fields  (shown in left hand side), and add it into 'Fields to Link' list box. Select the newly added field. Select the sub report parameter field name from 'Subreport parameter fields to use' combo box.

DONE..!!!