Abstract:  The inter-satellite link network plays an important role in BeiDou global short message system，one or more nodes of the constellation may fail during system operation or space confrontation，which will affect the availability of the global short message system.According to the characteristics of BeiDou short message service and inter satellite link，a global short message simulation analysis method based on inter satellite link is designed，20 different constellation fault scenarios are designed，and the loss of short message service in different scenarios and at different time is counted.The results show that when the total number of failed satellites in the short message payload is less than or equal to 2，there is almost no impact on the short message service area.When the number of failed satellites in the short message payload is 3.6，the loss of service area is less than 10%，which indicates that the global short message system based on the inter satellite link can still maintain high service availability with a few satellite failures.

Key words: Beidou satellites, global short message communication, inter-satellite link, fault simulation, service availability