High chemical reactivity, large volume changes, and uncontrollable lithium dendrite growth have always been the key problems of lithium metal anodes. Coating has been demonstrated as an effective strategy to protect the lithium metal. In this work, the effects of polyacrylonitrile (PAN)-based coatings on electrodeposited lithium have been studied. Our results show that a PAN coating layer provides uniform and dendrite-free lithium deposition as well as better cycling performance with carbonate electrolyte. Notably, heat treatment of the PAN coating layer promotes the formation of larger deposit particle size and higher coulombic efficiency (85％). The compact coating layer of heat-treated PAN with a large Young modulus (82.7 GPa) may provide stable protection for the active lithium. Improved homogeneity of morphology and mechanical properties of heat-treated PAN contribute to the larger deposit particles. This work provides new feasibility to optimize the polymer coating through rational modification of polymers.