The quantum confinement effect brings good field emission characteristics to silicon nanowires, which is expected to improve the performance of field emission device through combination with the quasiballistic electrons drift model in porous silicon structure, but the efficiency of traditional metal assisted chemical etching is low. Constant current source was introduced on the basis of traditional metal assisted chemical etching in the present work, and a electrocatalytic metal assisted chemical etching method was proposed to achieve high-efficiency preparation of silicon nanowires and porous silicon composite structure. The preparation rate of silicon nanowires is 308 nm/min at 30 mA current, which is increased by 173% compared with that adopted the traditional method. Moreover, the effects of AgNO₃ concentration, etching time and etching current on the morphology of the composite structure were investigated. The field emission characteristics of the structure prepared by electrocatalytic metal assisted chemical etching were tested. The current density is 64 μA/cm² under the electric field of 14.16 V/μm, and threshold electric field is 10.83 V/μm.