Transition metal sulfides (TMSs) have drawn promising attention due to their low cost and high theoretical capacity for sodium storage. However, the critical issues of TMSs with huge volume changes and lower ionic/electronic conductivity are the major challenges for their practical application in sodium-ion batteries. Herein, we constructed cobalt-doped ZnS encapsulated in an N-doped carbon shell (denoted as Co-ZnS@NC), which effectively alleviates the volume expansion and improves sodium storage performance. The mechanism analysis and ion diffusion kinetics analysis (GITT, EIS, and CV) prove the acceleration of Na+ diffusion by the built-in electric field and buffer carbon layer in the Co-ZnS@NC, optimizing the cycle life and rate capability. The as-prepared Co-ZnS@NC has a high reversible capacity of 456.8 mA h g-1 after 1000 cycles at 1.0 A g-1 and superior rate capability (368.8 mA h g-1 at 20.0 A g-1), with Na metal as the counter electrode. Moreover, the assembled full cell shows a high energy density of 214.4 W h kg-1. This work provides insight on heteroatom doping for optimizing the rate capability of TMS anodes.