Nanoencapsulated phase change materials were prepared through surfactant-free emulsion polymerization with n-octadecane (C18) and n-butyl stearate (BS) as binary cores and poly(methyl methacrylate) (PMMA) as shell. The effects of the type and dosage of emulsifier, the type and dosage of initiator and core/shell mass ratio on nanocapsules were studied. The surface morphology, chemical structure and thermal properties of phase change nanocapsules were characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). The results indicate that the best preparation conditions of nanocapsules are when the alkyl vinyl sulfonate (AVS) dosage is 3.0wt% to oil phase, ammonium persulfate (APS) dosage is 1.2wt% to MMA and core/shell mass ratio is 2:4. At the moment the monomer conversion of nanocapsules is the highest, particle size is the smallest and spherical morphology is the most regular. In addition, phase change nanocapsules have good latent heat storage capacity and heat resistance, and their melting enthalpy and crystallization enthalpy are 56.89 J/g and 54.02 J/g, respectively. The finished fabrics with phase change nanocapsules have better thermoregulation effect.