Recently, monitoring of existing tunnel environment has been increasingly more important due to the progressively risen public concerns, especially in extreme long tunnel like Hsuehshan tunnel in Taiwan. Such extreme long tunnel can easily cause significant hazard due to automobile accident. Therefore, developing an efficient and robust monitoring system to inspect the circumstances of tunnel is the momentous research. Capabilities of wireless sensor devices and networks have significantly more advantages over those of conventional monitoring instruments, which are wire-based systems for acquisitioning and transferring. Motivated by this, a study of design and integrating of wireless sensing system for monitoring existing tunnel situation is presented in this paper. The overall system design comprises two major units, a wireless sensing unit and a wireless receiving unit. Wireless sensing unit contains two functional modules, (1) sensing and data acquisition module; (2) microprocessor with wireless communication module. Only humidity, temperature, gas, light and photo sensors are investigated in this work, but any preferred sensor can be easily adopted with this smart transmitting scheme to realize a wireless sensor network system. Wireless receiving unit also consists of two functional modules, microprocessor with wireless communication module and a gateway. Experimental study was conducted to investigate the proposed prototype. Investigational results revealed that the feasibility of wireless sensor network in existing tunnel environment monitoring and maintaining.