Abstract: The existing codes and design guidelines for thin unstiffened steel plate shear walls (SPSWs) fail to evaluate the inelastic behavior of SPSWs under the maximum considered earthquake (MCE) level ground motion. Considering the ever-increasing demands of efficient and reliable design procedures, a performance-based plastic design method for slender unstiffened SPSW systems is proposed in this work, which sets a target drift and a preferred yield mechanism as its performance targets. Also investigated is the P-Δ effect on the seismic demand of SPSW. The design base shear for a given hazard level is derived based on the inelastic state of SPSWs, with the drift control built-in, by equating the work needed to push the structure monotonically up to the target drift to that requited by an equivalent elastoplastic single-degree-of-freedom (EP-SDOF) system to achieve the same state. The effectiveness of the proposed method is illustrated through the sample case study of a ten-storey SPSW building, and validated by pushover as well as dynamic elastic-plastic analyses. The addressed method herein can form a basis for the performance-based plastic design of SPSW systems.