Smart and green construction of noble metal nanostructures on two-dimensional nanomaterials-based flexible paper-like materials have gained extensive attention due to the formed hybrid papers have shown great promise in the applications of energy devices, sensing electronics, actuators, and chemical filters. Herein, a cost-effective and environment-friendly strategy to realize the spontaneous growth of noble metal nanoparticles (Au, Pd, and Pt) on flexible biomimetic MXene paper was proposed. The self-defined regulation of formed noble metal nanoparticles could be easily achieved, and the bimetallic (AuPt, PdPt) nanoparticles decorated MXene paper could be obtained at the mean time. These findings bring a simple, efficient and green way for constructing various hybrid MXene paper with outperforming electrocatalytic activities, which was demonstrated by the sensitive detection of superoxide (O) and the good stability and reproducibility after a long-term usage. The outstanding analytical performance of the obtained AuPtNPs/MXene paper in O monitoring leads to a satisfactory application in real-time extracellular biosensing. The investigation for spontaneous growth and regulation of noble metal nanoparticles on flexible biomimetic MXene paper exhibits a huge application potential for constructing high-performance flexible bioelectronics and energy-related devices.