Janus particles have garnered extensive attention owing to their considerable potential in the field of material engineering applications. Their properties are determined on the basis of the asymmetric structure or morphology. However, precisely engineering the morphology of Janus particles remains a grand challenge since the conventional preparation methods usually contain complicated dynamic processes. Herein, we report a facile route, which is wholly dependent on the thermodynamic characteristics of solution, to finely manipulate the morphologies of aqueous Janus droplets on a superhydrophobic surface. These Janus droplets contain polyethylene glycol (PEG) and dextran (DEX), and their Janus structures are controlled by the phase separation of the two polymers in aqueous solution. This phase separation procedure greatly relies on the molecular weight (MW) and concentration of PEG and DEX. As such, we can easily customize the morphology of the resultant Janus structure, including the Janus balance and curvature of the convex and concave phase interface, by varying those component inputs. This facile approach provides fresh insights into the tunable geometric morphology of Janus particles and holds potential applications in the preparation of asymmetric materials, particularly in biological fields.