The Real Time Publish Subscribe protocol (RTPS), as a Data Distribution Service (DDS) protocol for computer systems, is composed of several modules. We focus on RTPS StatefulWriter Module which has two patterns, reliable pattern and best-effort pattern. As the main module of sending and receiving messages, its security and reliability are of great concern. The formal method can analyze whether it is a highly credible model from the mathematical point of view. Our research pays attention to the reliable pattern. Thus it is of great importance to model and verify whether the pattern is reliable through formal methods. In this paper, we model seven components of the module using Communicating Sequential Processes (CSP). By feeding the models into the model checker Process Analysis Toolkit (PAT), we verify four properties, divergence free, acknowledgement mechanism, data consistency and sequentiality. Consequently, it can be apparently concluded that the pattern of this module is reliable, which totally caters for its specification.