Background Stroke-associated pneumonia (SAP) is a common and serious complication of acute ischemic stroke (AIS). The hemoglobin, albumin, lymphocyte, and platelet (HALP) score reflects nutritional, inflammatory, and immune status, but its association with SAP remains unclear. Methods We retrospectively analyzed 1,766 consecutive AIS patients admitted between January 2019 and December 2023. HALP was calculated from blood tests obtained within 48 h of admission. Multivariable logistic regression, receiver operating characteristic analysis, subgroup analysis, generalized additive modeling, and two-piecewise logistic regression were used to evaluate the association between HALP and SAP and to explore threshold effects. Results SAP occurred in 376 patients (21.3%). HALP was significantly lower in patients with SAP than in those without SAP [35.08 (18.59–51.86) vs. 44.55 (31.29–63.25), p < 0.001]. After full adjustment, each 1-unit increase in log2-HALP was associated with a 29% lower SAP risk (OR = 0.71, 95% CI: 0.62–0.83, p < 0.001). The highest HALP quartile was associated with a lower SAP risk than the lowest quartile (OR = 0.62, 95% CI: 0.41–0.95; P for trend = 0.018). A non-linear association was identified, with an exploratory threshold at HALP approximately 27.7. Below this threshold, each log2-unit increase in HALP was associated with a 53% lower SAP risk (OR = 0.47, 95% CI: 0.35–0.63, p < 0.001), whereas no significant association was observed above it. Adding HALP to the A2DS2 score produced a statistically significant but modest improvement in discrimination (AUC: 0.758 vs. 0.779, p = 0.004). Conclusion Low HALP score was independently and non-linearly associated with SAP in AIS, with an exploratory threshold near 27.7 that may help inform future risk-stratification research.