Background <p>Early detection of cognitive dysfunction (POCD) in patients undergoing cardiac surgery may help improve the prognosis and quality of life. Identifying risk factors and clinically relevant factors is critical for prevention and treatment.</p> Methods <p>This study retrospectively selected 305 patients admitted to the cardiac surgery Department of Union Hospital Affiliated with Fujian Medical University from January 2024 to July 2024 as the study objects. The cognitive function of the patients was assessed by the Montreal Cognitive Assessment Scale (MOCA) before and on the 6th day after surgery, and the patients were divided into a cognitive dysfunction group and a non-cognitive dysfunction group. Logistic regression was used to analyze the risk factors of POCD in patients undergoing cardiac surgery. R software was used to construct the nomogram model of POCD in heart patients.</p> Results <p>Logistic regression model was used to screen the included variables, and the final results showed age (<i>OR</i> = 2.670, 95%CI 1.675–4.255,<i> P</i> &lt; 0.001), white blood cell count (<i>OR</i> = 1.155, 95%CI 1.050–1.271, <i>P</i> = 0.009), lymphocytes (<i>OR</i> = 2.200, 95%CI 1.512–3.200, <i>P</i> &lt; 0.001), and hemoglobin (<i>OR</i> = 1.020, 95%CI 1.009–1.032,<i> P</i> &lt; 0.001) were independent risk factors for POCD on day 6 in patients undergoing cardiac surgery. The predicted value of the calibration curve of POCD on the 6th day of cardiac surgery was consistent with the actual value, and the Hosmer–Lemeshow goodness-of-fit test (<i>χ</i>² = 8.73, <i>P</i> = 0.36 &gt; 0.05) showed good consistency. The area under the ROC curve is 0.80, with a good differentiation and decision curve.</p> Conclusions <p>Age, white blood cell count, lymphocyte, and hemoglobin are independent risk factors for POCD on day 6 of cardiac surgery. The nomogram prediction model constructed in this study has good predictive ability.</p>