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Conductive polymer composites have attracted attention for their tunable electrical conductivity and microwave shielding performance by controlling the distribution of conductive fillers. In this work, the effect of processing temperature on the distribution of multiwall carbon nanotubes (MWCNTs) in the high density polyethylene/poly(ethylene‐co‐1‐octene) (HDPE/POE) composites was investigated. The MWCNTs were premixed with HDPE to form HDPE/MWCNT master batches at 180°C, and then mixed with POE at different temperature of 140°C and 210°C. At high temperature of 210°C, the volume diffusion of MWCNTs would easily happen in the composites which made the MWCNTs be randomly dispersed in both HDPE and POE domains. At low temperature of 140°C, the MWCNTs could hardly diffuse from HDPE phase to POE phase because of the high viscosity of polymer matrix. Therefore, most of MWCNTs were confined dispersion in HDPE in the composites being prepared at low temperature, which exhibited high electromagnetic interference (EMI) shielding performance and high conductivity. Specifically, the electrical conductivity of the HDPE/POE (58/42 v/v)/MWCNTs composites with 2.5 vol% MWCNTs increased from 7.4 × 10−2 to 0.78 S/m at the mixing temperature of 210°C and 140°C, respectively. The average EMI shielding effectiveness (SE) of the HDPE/POE (58/42 v/v)/MWCNTs composites with 4.0 vol% MWCNTs increased from approximately 19.7 to approximately 26.7 dB at the mixing temperature of 210°C and 140°C, respectively. This works provide a processing temperature controlling strategy to fabricate conductive polymer composites with high‐performance microwave shielding. [ABSTRACT FROM AUTHOR]