【Objective】 To analyze the clinical features of nonvalvular atrial fibrillation （NVAF） patients with left atrial/left atrial appendage spontaneous echo contrast （LA/LAASEC）， and investigate the correlation between LA/LAASEC and left atrial diameter. 【Methods】 Clinical data （including gender， age， and history of hypertension， diabetes， stroke or transient ischemic attack， vascular disease）， laboratory indexes （including coagulation indicators， blood routine， thyroid function）， and transthoracic echocardiogram parameters of 262 NVAF patients hospitalized in the Department of Cardiovascular Medicine of our hospital from November 2019 to January 2021 were collected and analyzed retrospectively. According to the results of transesophageal echocardiography， they were divided into control group and LA/LAASEC group. Logistic regression analysis was performed to investigate the influencing factors of LA/LAASEC. ROC curve analysis was used to evaluate the predictive value of left atrial diameter for LA/LAASEC. 【Results】 The proportion of non-paroxysmal atrial fibrillation was significantly higher in LA/LAASEC patients than the controls （65.9% vs. 32.2%， P<0.01）， and so was the CHA2DS2-VASC score （P=0.003）. Compared with the control group， left atrial diameter and left ventricular end-systolic/end-diastolic diameters were significantly increased， left ventricular ejection fraction was significantly decreased， and the level of NT-proBNP was significantly increased in LA/LAASEC group （P<0.05）. Logistic regression analysis showed that non-paroxysmal AF （OR=2.451， 95% CI： 1.260-4.766， P<0.05）， CHA2DS2-VASc score （OR=1.236， 95% CI： 1.023-1.494， P<0.05）， and left atrial diameter （OR=1.086， 95% CI： 1.019-1.157， P<0.05） were independent risk factors for LA/LAASEC. ROC curve analysis displayed that the AUC for left atrial diameter in predicting LA/LAASEC was 0.731 （95% CI： 0.668-0.794， P<0.001）. 【Conclusion】 Left atrial diameter is closely related to LA/LAASEC in NVAF patients. Combined with atrial fibrillation type and CHA2DS2-VASC score， it has a potential value in predicting the risk of thromboembolism in NVAF patients.