This article describes the prototype of the read-out subsystem which will be subjectto the BESIII data acquisition system. According to the purpose of the BESIII, the event rate willbe about 4000 Hz and the data rate up to 50 Mbytes/sec after Level 1 trigger. The read-out sub-system consists of some read-out crates and a read-out computer whose function is to initialize thehardware, to collect the event data from the front-end electronics after Level 1 trigger, to transferdata fragments to the computer in online form through two levels of computer pre-processing andhigh-speed network transmission. In this model, the crate level read-out implementation is basedon the commercial single board computer MVME5100 running the VxWorks operating system.The article outlines the structure of the crate level testing platform of hardware and software. Itputs emphasis on the framework of the read-out test model, data process flow and test method atcrate level. Especially, it enumerates the key technologies in the process of design and analyses thetest results. In addition, results which summarize the performance of the single board computerfrom the data transferring aspects will be presented.