Mock equation of state I am student of astrophysic i need to meaning of "mock equation of state".
And is there any specific way to generate mock equation of state. 
 A: I guess that what is meant is a relationship between the pressure of the gas and it's density, temperature and composition.
No, there is no specific way to make something that you have defined in a completely general way, without describing any context - is this a star, a compact object, the interior of a star forming cloud, an ionised nebula?
A mock equation of state for a neutron star might be 
$$P = A\rho^{\alpha},$$
where $P$ is pressure, $\rho$ is density and $A$ and $\alpha$ are constants of your choosing to reflect you chosen physics. You might even have several different $A,\rho$ value in different density intervals to cope with changes in the equation of state and composition that are made such that $P$ vs $\rho$ forms a continuous relationship.
For example, an ideal degenerate gas of electrons (accompanied by ions, say in a white dwarf) obeys $P \propto \rho^{5/3}$ at low densities, but become $P \propto \rho^{4/3}$ at higher densites. Then when neutronisation takes place the gas pressure again becomes dominated by non-relativistic neutrons with $P \propto \rho^{5/3}$, but if a neutron gas become relativistic then $P \propto \rho$.  Alternatively you might adjust the value of $\alpha$ to reflect a (non-ideal) hardening of the equation of state due to nucleon repulsion at high densities by allowing $\alpha \rightarrow 2$.
