In this work, rapid chemical precipitation assisted annealing method is used to prepare flower-like NiCo2S4. And the flower-like structure after polyethylene glycol (PEG) modification yields an excellent specific capacitance (2198.9 F g-1 at 1 A g-1). And an asymmetric supercapacitor assembled with NiCo2S4 (PEG-modified) and activated carbon (AC) shows an energy density of 38.2 Wh kg-1 at 400 W kg-1, and outstanding stability (80% remained after 3000 cycles at 5 A g-1). Benefited by a larger specific surface area and suitable pore size of the aggregate structure, the specific capacitance of prepared NiCo2S4 is increased by about 2 times. This uncomplicated preparation method is proved to be suitable for NiCo2S4 with a high specific capacitance of supercapacitors.