TLI is a programming interface to the transport layer of ISO-OSI model，it supports the transfer of data between two user processes in network. TLI provides two modes of service for application and development；connection mode and connectionless mode. The former is appropriate for applications that requires relatively long-lived，datastream-oriented interactions; the latter is appropriate for application that involves short-term request/response interactions. In this paper，the auther discussed connetionless mode service of TLI and several problems that must be solved.