Objective: To report and explain the significance of transesophageal echocardiography(TEE) in the observation of left atrium and left atrial appendage before radiofrequency ablation in patients with AF. Methods: 25 patients with AF were selected as the review objects who received echocardiography in our hospital during June 2018 to June 2019. They had routinely received transthoracic echocardiography (TTE) before preparing for radiofrequency ablation. Then TEE was selected to observe and compare the effect of two detection methods on left atrial and left auricular thrombosis. Results: TEE examinations were given to patients with atrial fibrillation before radiofrequency ablation. Compared with TTE examinations, the detection rate of left atrium and left atrial appendage thrombosis was significantly improved. The two detection methods are different and comparable(P<0.05), which is of great significance in clinical application. Conclusion: The use of TEE has significantly improved the detection rate of left atrial and left atrial appendage thrombosis in patients with AF, and has become an important examination method before the implementation of radiofrequency ablation.