Objective To explore the clinical features of left atrial spontaneous echo contrast (LASEC) in patients with persistent atrial fibrillation (AF) and to analyze its correlation with left atrial sphericity index (LASI). Methods Clinical data of 96 patients with nonvalvular persistent AF admitted to our hospital from August 2021 to December 2022 were collected and retrospectively analyzed. These patients were divided into LASEC group (n=54) and control group (n=42) according to the results of echocardiography. Their comorbidities, results of laboratory tests, cardiac ultrasound parameters and LASI were compared between the two groups. SPSS statistics 22.0 was used to perform the statistical analysis. Student′s t test, Mann-Whitney U test or Chi-square test was employed for intergroup comparison depending on data type. Pearson correlation analysis was applied to explore the correlation of LASI with comorbidity and echocardiographic parameters. Logistic regression analysis was conducted to investigate the risk factors of LASEC. Results The proportion of female patients, CHA2DS2-VASc score, D-dimer level, N-terminal pro-B-type natriuretic peptide (NT-proBNP), LA anteroposterior diameter and transverse diameter, and LASI were significantly higher in LASEC group than the control group (P<0.05). LASI was positively correlated with body mass index (BMI) , heart failure and left ventricular end-diastolic diameter (r=0.236,0.727,0.212; P<0.05), and negatively with left ventricular ejection fraction (r=-0.225, P<0.05). Higher CHA2DS2-VASc score (OR=1.637,95%CI 1.117-2.400), elevated D-dimer level (OR=1.006,95%CI 1.002-1.010), and increased mean LASI (OR=3.556,95%CI 1.704-7.424) were risk factors for LASEC. Conclusion LA sphericity is an causal risk factor for LASEC in patients with persistent AF. The mean LASI can well indicate LASEC, with a promised prospect for clinical application.