The invention provides an establishing method and device for a homo-polar crossing fault model between DC systems, which relate to the field of electric power systems, and can establish a homo-polar crossing earth fault equivalence model between DC systems. The method comprises the steps of obtaining the homo-polar crossing earth fault model by means of Thevenin equivalence; conducting simulationon the earth fault model for obtaining a fault network topological diagram; establishing a fault boundary equation set based on the fault network topological diagram and the preset rule; obtaining thetriggering angle value of a converter station in the fault network topological diagram based on the simulation result of the earth fault model; establishing the homo-polar crossing earth fault equivalence model based on the dynamo-electric transient simulation rule; calculating the fault equivalence impedance value of the homo-polar crossing earth fault equivalence model based on the triggering angle value of the converter station in the fault network topological diagram, the fault boundary equation set, and the preset rectifiying-side equation set.