The blocking process of the geotextile tube in the closure gaps is obviously affected by hydraulic force，and the geotextile tube is prone to slip and instability，which leads to the failure of the blocking of the junctions，resulting in increased construction costs and delays in the construction period. To reduce the risk of the failure，based on the theoretical analysis，this paper uses the FLOW 3D and FLAC 3D numerical simulation software to analyze the stability of the weir top geotextile tube，and compares it with the actual project. The results show that：1）The hydrostatic pressure and the horizontal thrust of the water flow generated by the overflow at the top of the weir are the main factors for the slip failure of the top geotextile tube. 2）The sliding critical head is positively related to the width of top bag，the equivalent friction coefficient between bags and the weight of bag filling. 3）The calculation results of the prediction formula are more consistent with the actual engineering，and have certain engineering reference value.