The present invention discloses a method and device for studying fluid equilibrium distribution in heterogeneous oil and gas reservoirs. Firstly, a reservoir is divided into multiple layers according to permeability of the reservoir; a pressure-depth curve of formation water in surrounding rock is established; the pressure-depth curve of a non-wetting phase is made by passing through a point in the reservoir and taking a product of density and acceleration of gravity of the non-wetting phase as a slope; the pressure-depth curve of displacement pressure of the reservoir is added on the basis of the pressure-depth curve of the formation water; and the pressure-depth curve of the non-wetting phase is repeatedly compared with the pressure-depth curve of the displacement pressure to obtain static equilibrium distribution of fluid in the reservoir.