At present，the studies on dynamic mooring analysis and impact force of vessels under beam seas all focus on large-scale wharves，and no study pays attention to tugboats. Therefore，on the basis of an auxiliary tugboat berth project of a container terminal in Southeast Asia，the analysis of dynamic mooring stability and impact force of tugboats under beam seas are studied in this paper. The dynamic mooring analysis software aNyMOOR TERMSIM is adopted to calculate the dynamic mooring stability under beam seas，and the impact force，mooring force，and vessel motion are obtained from the calculation under normal use and extreme conditions. The result of the impact energy is compared with that from the Load Code for Harbor Engineering of China，and the regulations on the mooring conditions and motion of small vessels from different design codes at home and abroad are compared and analyzed. As a result，the recommended standards for waves and motion of tugboats are given in combination with this project. The results reveal that for small vessels like tugboats，the impact energy calculated by dynamic mooring analysis software is about 2.3 times greater than that from the Chinese design code. Under extreme conditions，the traditional DA fender or V-shaped fender could not meet the demand of wharf structure；instead，drum-shaped or conical fenders are more suitable for economic and rational wharf structure. Moreover，it is recommended that regarding the surge and sway amplitude，the motion of tugboats should be less than 1.5 m and 1.0 m under normal operation conditions and less than 2.0 m and 1.5 m under extreme conditions，respectively. The recommended limit of the beam sea height is less than 0.4 m under normal operation conditions and less than 1.4 m under extreme conditions.