Flexible electronic devices have received increasing attention for potential application in wearable human motion monitoring, healthcare and thermal management. Nevertheless, flexible electronic devices for more precise health monitoring of human physiological movement under low strain are still a pressing issue to be solved. Herein, wearable flexible strain sensor with the 3D conductive network is developed for healthcare monitoring and thermal management by embedding silver nanowires (AgNWs) and Ti3C2Tx MXene composite films into a polydimethylsiloxane (PDMS) matrix. The sensor can be utilized for human health monitoring, pulse detection at the wrist, and breathing monitoring of human physiological movement due to its low strain detection capacity (0.05% strain) and high sensitivity (gauge factor up to 9472). The primary detection range of sensor is 0 to 1% of tiny strains. Moreover, the exceptional electric heating and optothermal effect supported by AgNWs and MXene protects human health in extremely cold environment. The MXene/AgNWs strain sensor with high sensitivity under low strain has great potential for more precise health monitoring of human physiological movements and thermal management.