Objective To analyze the accuracy and influencing factors of miniprobe ultrasonic endoscope in evaluating submucosal infiltration of colorectal laterally spreading tumor (LST).Method A retrospective analysis was conducted on the clinical data of 213 patients (268 lesions in total) with colorectal LST who underwent endoscopic submucosal dissection (ESD) treatment from June 2018 to August 2021. We summarized the clinical pathological characteristics and miniprobe ultrasonic endoscope examination results of LST, then analyzed the accuracy of miniprobe ultrasonic endoscope examination and the risk factors affecting the accuracy of miniprobe ultrasonic endoscope examination.Results The accuracy rate of miniprobe ultrasonic endoscope examination was 93.28%, and there was a statistically significant difference in the accuracy rate of miniprobe ultrasonic endoscope examination between different lesion surface morphologies (P = 0.000). Multivariate Logistic regression analysis showed that mix-ed nodule and false depression lesions were risk factors for inaccurate EUS assessment.Conclusion Colorectal LST is a special type of tumor, and miniprobe ultrasonic endoscope examination has a high accuracy in evaluating its infiltration depth. The surface morphology of the lesion is a risk factor that affects the accuracy of miniprobe ultrasonic endoscope examination. When the lesion is a nodule mixed type or pseudo depressed type, it can easily lead to inaccurate miniprobe ultrasonic endoscope examination.