A preparation method for a fused tricyclic γ-amino acid derivative and an intermediate thereof, and a method for preparing an intermediate of the fused tricyclic γ-amino acid derivative. The fused tricyclic γ-amino acid derivative has a structure as represented by formula (I). The preparation method uses readily available raw materials and comprises simple steps; the entire synthesis process uses crystallization purification, while silica gel column chromatography or other preparatory chromatography methods are not used, being suitable for large-scale industrial production.