The present application relates to a device for preparing an electrode assembly and a preparation method of the electrode assembly. Wherein the device for preparing the electrode assembly includes: a winding assembly; a plurality of first electrode plate unwinding apparatuses, configured to provide a plurality of first electrode plates for the winding assembly; and at least one second electrode plate unwinding apparatus, configured to provide at least one second electrode plate for the winding assembly, wherein a polarity of the first electrode plate is opposite to a polarity of the second electrode plate; and wherein the winding assembly is configured to wind the plurality of first electrode plates and the at least one second electrode plate, to form an electrode assembly. The present application is used for improving winding efficiency of the electrode assembly.