Maintaining colloidal stability in unfriendly environments such as high salt content or high temperature, while retaining surface chemical properties is challenging for fundamental science and many applications. We invented a method to stabilize nanofluid of graphene-based amphiphilic Janus nanosheets under salt condition which has higher ionic strength than seawater (on average, containing 3.5 wt% NaCl). By simply mixing certain amounts of polyelectrolytes, e.g., poly(sodium 4-styrenesuflonate), and amphiphilic Janus nanosheets in brine, the nanofluid can be prepared stably while the interface behavior of the nanosheets retained as the same as we observed in fresh water dispersed system when oil phase was co-existent. Nanofluid of amphiphilic Janus nanosheets can be used for enhanced oil recovery. Salt water dispersed nanofluid can be further beneficial for saving huge amounts of fresh water and reusing the produced formation water, thereby reducing the cost of waste water treatment. Moreover, it can be injected for oil recovery in water-sensitive oil reservoirs where fresh water dispersed nanofluid lacks. In addition, the method may be also applicable to other amphiphilic Janus nanomaterials.