To compare the effects of minimally invasive cardiopulmonary bypass coronary artery bypass grafting (MICB-CABG) and conventional cardiopulmonary bypass (CCPB)-CABG on the occurrence of atrial fibrillation (AF), in this research, totally 86 patients with CABG, admitted in our hospital from March 2020 to October 2021, were selected and divided equally into MICB-CABG and CCPB-CABG groups, according to the random number table method. The incidence of AF and left atrial volume index (LAVI) were compared between the two groups. In total, 104 patients with symptoms such as chest tightness, breathlessness, chest pain, and precordial discomfort were included in the study. All patients were examined by nano-CT and coronary angiography. However, time of ventilator use and time of fever were shorter in the MICB-CABG group. AF is closely related to LAVI, and levels of inflammatory factors, such as high-sensitivity (hs)-CRP, IL-6, and tumor necrosis factor-α (TNF-α), in the CCPB-CABG group were significantly higher than those in the MICB-CABG group. Taking the results of selective coronary angiography as the gold standard, the sensitivity and specificity of nano-CT in detecting coronary artery abnormalities were 99.17% and 97.93%, respectively, suggesting that nano-CT can display coronary artery variations precisely. Compared with the CCPB-CABG group, the incidence of AF after surgery and the risk indicators related to the occurrence of AF were significantly lower in the MICB-CABG group. Compared with traditional CCPB-CABG, MICB-CABG interferes less with the physiological functions of the body, reduces atrium damage, and improves the therapeutic effect. In addition, magnetic nanoparticle CLIA can meet the clinical need for detecting serum indexes and has good potential for clinical use.