In this paper, hydrophobic PAN/SiO 2 −PU composite nanofiber membranes were prepared by coaxial electrospinning combined with a hydrothermal method. The effects of the feeding rate ratio of the shell (PAN/SiO 2 ) solution and the core (PU) solution, the content of SiO 2 in the shell solution, and the hydrothermal time on the composite nanofiber membrane were analyzed. The results showed that when the feeding rate ratio of the shell−core solution was 5:1 and the SiO 2 content in the shell solution was 60 mg•mL −1 , the PAN/SiO 2 −PU nanofiber presented a uniform diameter and an obvious shell−core structure, and the Si element was uniformly distributed on the fiber surface. After hydrothermal treatment, the surface water contact angle of the PAN/SiO 2 −PU composite nanofiber membrane reached 152°, and the water vapor transmission rate was 8.48 kg•m 2 •d −1 . In addition, the average solar reflectance of the composite nanofiber membrane was as high as 60.29%, and the temperature difference between the PAN/SiO 2 −PU and PAN−PU composite nanofiber membranes was 4.5 °C, indicating an obvious radiative cooling effect.