A FinFET device structure and method for forming the same are provided. The FinFET device structure includes a first fin structure extending above a substrate, and the first fin structure includes a portion made of silicon germanium (SiGe). The FinFET device structure includes a second fin structure adjacent to the first fin structure. The FinFET device structure also includes a first liner layer formed on the outer sidewall surface of the first fin structure and a second liner layer formed on the inner sidewall surface of the first fin structure. The FinFET device structure further includes a first isolation structure formed on the substrate, and the first liner layer is between the first isolation structure and the first fin structure, and a top surface of the second liner layer is higher than a top surface of the first liner layer.