Objective　To measure the lower abdominal wall thickness in adults，explore its correlation factors，and its significance for the micturition alert device on the principle of a compass.　Methods　The thickness of the lower abdominal wall, including its superficial and deep layers, the maximal anteroposterior, laterolateral and craniocaudal diameters of the bladder were measured respectively using ultrasound skill in 100 adults. As well, the weight, height and body mass index (BMI) was measured and determined, followed by the calculation of the bladder  volume. The correlation factors contributing to the lower abdominal wall thickness were analyzed.　Results　The thickness of the lower abdominal wall was about (23.4±6.6)mm, with 95% confidence interval of 22.1～24.7mm. The thickness was positively correlated with the thickness of superficial and deep layers of the lower abdominal wall, the weight, BMI and the distance from the measuring point to umbilicus, and was negatively correlated with the volume, laterolateral and craniocaudal diameters of the bladder. There was no correlation of the lower abdominal wall thickness with gender, age, height and anteroposterior diameters of the bladder.　Conclusions　For the adults, the thickness of the lower abdominal wall is about (23.4±6.6)mm under ultrasound machine. Nutritional status is the most important correlation factor of the lower abdominal wall thickness. The results provide a new evidence for the usage and improve of the micturition alert device on the principle of a compass