I create a BT to retrieve a parameter in a user action A, if this situation happens, I'd like to check the whole visit if user action B exist, is that possible?
The perfect scene for me is to put parameter in Splittings and other user actions in calculate results
(show counts, if exist, >=1)
Maybe I am not understanding this right, but I think the way you want to use this parameter would be as a Filter, not a Splitting.
First off, you're going to want to select Visit as your Calculate Business Transaction per.
Now let's pretend you've created your User Action A measure based on whatever parameter you have.
Set the Upper Severe threshold for your User Action A to 1. This is what you will use as the filter for your BT. This is basically doing as you asked, if this user action exists in the visit, then include it in the BT.
Next is a little tricky.
You could add another filter for User Action B (using the same threshold), the count of your Visit Count will then reflect how many visits had both of these user actions in them.
The other option you have is to use User Action B (using the same threshold) as the Result and set it to count. In this situation you could compare the Visit Count to the User Action B count to determine how many visits had User Action B at least once and how many did not.
I'm not sure what your reason for building this BT is, so I can't say which is going to be the better option or if it's going to achieve what you want it to.
Let me know if that helps or you have any questions,