Got the answer from MS KB

COMPILE FORM LibName


>In VFP 3.0, type COMPILE CLASSLIB LibName
>
>It will now work in VFP 3.0 as long as there isn't any VFP 5.0 specific code.
>
>>Can a VFP5 vcx be complied to work in VFP3?
>>
>>(I need to use VFP3 bec dev requires Win 3.11)