The invention discloses a nano heterojunction solar cell based on a chalcogenide cuprous compound and a preparation method thereof. The nano heterojunction solar cell based on the chalcogenide cuprous compound is characterized in that a silicon substrate whose upper surface is covered with an insulating layer serves as a substrate, a chalcogenide cuprous compound quasi-one-dimensional nano-structure is dispersed on the insulating layer, a first metal film electrode and an In2S3 film are deposited respectively on two ends of the chalcogenide cuprous compound quasi-one-dimensional nano-structure, the chalcogenide cuprous compound quasi-one-dimensional nano-structure is in ohmic contact with the first metal film electrode and forms a heterojunction with the In2S3 film, a second metal film electrode is deposited above the In2S3 film, the In2S3 film is in ohmic contact with the second metal film electrode. According to the invention, the nano heterojunction solar cell completely uses environmental-friendly inorganic semiconductor materials, the preparation process is simple and easy, and the device performance is superior.