The invention relates to a preparation method of a Janus-structure composite 
emulsion particle. The method comprises the following steps: adding deionized water into a PVDF seed 
emulsion, performing 
ultrasonic dispersion for 1 hour, pouring the dispersed 
emulsion into a reactor equipped with a 
reflux condensing tube, a stirring device, and a 
nitrogen introducing port, starting stirring and continuously introducing 
nitrogen, after 15 min, heating the 
reaction system, adding monomers, introducing cooling water into the 
reflux condensing tube; when the 
system is heated to a 
reaction temperature, adding an initiator, performing a 
polymerization reaction at a 
reaction temperature of 20-80 DEG C for 1-8 hours; 
drying the emulsion at a reduced pressure and a low temperature to obtain a constant weight so as to obtain the Janus-structure composite particle. Through the selection of PVDF seeds with different particle sizes, the seed 
monomer mass ratio and the 
polymerization time, the invention can effectively control the form and the size of the composite particle. The invention is widely applicable to various fields in 
polymer blending modification, such as compatilizers, self-cleaned coatings, and the like.