How can I pass lookup field value from form1 to form2?

-Form1 and Form2 both has lookup field to form0.

-Report of Form1 has custom action button which "openurl" of Form2.

-When Form2 is called from Form1 custom action, I want to pass Form1's  Form0 ID to Form2 as a default value.

I tried like  "openUrl(" https://...#Form:form2" + "?form0=" + form1.form0, "Same window");"

but form2's lookup field to form0 is null.

How can i pass lookup field value in openurl method?

Thanks 

Tadashi