The equilibrium lattice parameter, heat capacity, thermal expansion coefficient and bulk modulus of Ni2MnGa Heusler alloy are successfully obtained using the first-principles plane-wave pseudopotential (PW-PP) method as well as the quasi-harmonic Debye model. We analyse the relationship between bulk modulus B and temperature T up to 800 K and obtain the relationship between bulk modulus B and pressure at different temperatures. It is found that the bulk modulus B increases monotonically with increasing pressure and decreases with incrcasing temperature. The pressure dependence of heat capacity Cv and thermal expansion a at various temperatures are also analysed. Finally, the Debye temperature of Ni2MnGa is determined from the non-equilibrium Gibbs function. Our calculated results are in excellent agreement with the experimental data.