In arid and semi-arid farmlands, polyethylene residual film (PRF) poses a serious threat to soil ecological functioning. In agricultural practices, PRF frequently coexists with straw. However, the mechanism underlying their synergistic effects on soil organic carbon (SOC) turnover remains unclear. To investigate this, 13C stable isotope tracing, 16S/ITS absolute quantitative sequencing, and amino sugar biomarker analysis were employed to elucidate the mechanisms of SOC turnover under PRF addition alone [0.06 % (R1) and 0.12 % (R2), w/w] and in coexistence with straw [1.2 % (S), w/w]. PRF alone (R1/R2) significantly suppressed fungal abundance, reducing fungal ITS rRNA gene copy numbers by 21.46 % and 21.94 %, respectively, which in turn decreased fungal necromass carbon by 12.86 % and 3.32 %. In contrast, the coexistence of PRF and straw (SR1/SR2) generated heterogeneous microsites through the combined effects of PRF hydrophobicity and straw porosity. This enhanced the priming effect and promoted straw decomposition. Meanwhile, these changes were accompanied by 8.94 % and 3.41 % increases in fungal abundance and fungal necromass carbon, respectively, ultimately stabilizing SOC. Notably, under SR2, physical degradation and weak carbonyl peaks indicated early-stage plastic degradation. Overall, straw alleviates PRF-induced fungal suppression, transforms PRF from pollutant to structural modifier, and reshapes microbial necromass carbon pathways, promoting SOC retention.