Objective To investigate the relationship of insulin resistance (IR) with the severity of coronary calcification and determine the effect of IR on prognosis in the elderly patients with non-ST segment elevation acute coronary syndrome (NSTACS). Methods A total of 150 consecutive elderly patients (≥60 years old) with NSTACS admitted in our department from June 2013 to June 2014 were enrolled in this study. Based on their IR index measured by homeostasis model assessment (HOMA), they were divided into the IR group (HOMA-IR＞5.0, n＝80) and non-IR group (HOMA-IR≤5.0, n＝70). All patients received 320-detector row computed tomography scanning to calculate coronary calcium score (CCS) before percutaneous coronary intervention (PCI). These patients were followed up for 12 months, and the occurrence of major adverse cardiac events (MACE) were recorded. Results The levels of fasting plasma glucose (FPG), fasting insulin (FINS), low density lipoprotein-cholesterol (LDL-C), high sensitivity C-reactive protein (hs-CRP) and homocysteine (Hcy) had significant discrepancies between the patients of IR and non-IR groups (P＜0.05). Spearman correlation analysis showed that HOMA-IR was positively correlated with CCS in the elderly NSTACS patients (r＝0.393, P＜0.01). In 12 months of follow-up, multivariate logistic regression analysis showed that HOMA-IR＞5.0, CCS＞400, New York Heart Association (NYHA) classification grade Ⅲ-Ⅳ and diabetes were independent risk factors for MACE in the elderly NSTACS patients after PCI (P＜0.05). Kaplan-Meier survival analysis indicated that the cumulative survival rates was significantly lower in the IR group than in the non-IR group (Log rank＝4.755, P＝0.029). Conclusion The elderly ACS patients with IR have more serious coronary calcification. IR and CCS are of predictive value for the prognosis in the elderly NSTACS patients undergoing PCI.