Nowadays, crack-based stretchable strain sensors (CBSSS) has being attracted intensive attention because they enable sensors to realize high sensitivity and wide sensing range. However, simultaneous achieving the excellent sensing performance and environmental stability of CBSSS is still a great challenge. In this study, microtube strain sensor decorated with microcracks on the inner wall (MSS-CIW) was fabricated, whose outer layer and inner wall are respectively TPU and MWCNTs based microcracks. Of note, such unique architecture not only endows the sensor with higher sensitivity (maximum " role="presentation"> of 26358) and a wider sensing range (strain from 0-400%), but also effectively prevent the encroachment of external environments (e.g., water, chemicals and friction). Therefore, MSS-CIW has excellent static/dynamic environmental stability, durability and abrasion resistance. Moreover, based on MSS-CIW, a wearable underwater wireless monitoring system has been developed, which can be used for underwater communication, underwater respiration monitoring and fish motion monitoring. This work proposes a facile and efficient method for fabricating high sensing performance CBSSS that can work under severe environments, opening a new pathway to develop stretchable strain sensors following the concept of "Functionalized Processing for Thermoplastic Polymers".