>How can I user VFP Class(VCX) in Visual BAsic 6?

You can't directly do so. You can compile the VFP VCX to be a COM Component of some sort (it can be either a .DLL, creating an in-process server, or a .EXE, which would be an out of process server.) Once it is compiled as a server and registered, it can be used like any other COM component.

A couple of things to realize:

(1) You will need the VFP runtime installed on each system that instantiates a VFP COM server. If you access the VFP COm component via DCOM (either an out-of-process server running on another machine, or an in-process server controlled by MTS running on another machine), only the server machine(s) require the VFP runtime.

(2) You cannot integrate user interface components from VFP into another application using a VFP COM object. VFP-created in-process servers cannot have any user interface elements at all, and out-of-process servers, while they may have user interface elements, cannot have them incorporated into the client app's event loop. IOW, you can't create controls from VFP.