How to calculate this characteristic impedance?

In genernal,when we calculate the microstrip's characteristic impedance,the top plane is microstrip and the bottom is GND plane ,and between them is dielectric.But now I want to add a VCC plane between the top and bottom plane,then how to calculate the characteristic impedance?Is the H the distance between the top and the VCC?

If the VCC plane is properly bypassed to ground, this becomes a stripline. You should easily find information about this type of transmission line.

I don't think it as stripline.
That is the top plane is signal ,and inner plane is VCC,then the bottom plane is GND.I want to konw the characristic impedance of the signal line not the VCC..............help

You're correct in assuming the VCC plane as the return path for the energy. It should behave (on a first order) like a microstrip referenced to the VCC plane (this assumes the VCC plane fully serves as the return path - i.e. wider than the RF trace).

On a second order approximation there will be some energy coupled to the VCC plane and to the GND plane.