How to Calculate EMI Filter Component Value

I assume that you understand how to apply Kirchoff's laws and can perform a mesh or nodal analysis. You also will have to apply superposition theory.

An EMI filter network should be designed to handle two sources of interference, interference from the power distribution grid into the power supply/load circuitry and interference into the power distribution grid from the power supply/load circuitry. Now the loading circuitry on your power supply side of your sketch is well known and controllable by the circuit designer. In contrast, the loading by the power distribution network on the filter network to reduce the noise from the supply back to the grid is not known nor controlled by the designer. So some assumptions must be made by designer about the grid impedances. (Your diagram shows an ideal battery, a Norton or Thevenin equivalent must be used.) When you take this all into account, a minimum capacitance will be desired at C_x to meet your design goal.

That's the basic idea.

Really did not get you mate :)

Do you understand my first two sentences? Specifically do you know how to construct a mesh analysis from Kirchoff's rules?

ya i know how to do mesh analysis but how it will help me to find the value of X-cap?

So you claim to know how to generate a transfer function but you do not know how to allow this function to solve for the value of a component.

I'm speechless.

please help me out :(

I don't know why I'm trying to help you here. It appears you are not willing to help yourself. I will not spoon feed you an equation. I gave you a batch of information and you've only acknowledged one part but you've not demonstrated that you actually do understand Kirchoff's laws and mesh or nodal analysis. So I'll ask another question to see if you understand what I've already given you.

Should you substitute a Thevenin or Norton sub-circuit for your battery to do a precise analysis and why?

Maybe I should save some time by asking some more leading questions. What are the nominal or measurable parasitic components for the capacitors and inductor that convert a wiring schematic to an analysis schematic? Which parasitic components can and cannot be ignored in this configuration and why?