Sodium alginate (SA), as the eco-friendly and human-safe biomass material not only can achieve effective dispersion of graphene nanoplatelets (GnPs), but also improve the interaction between GnPs and cellulose macromolecules. Based on this, a flexible and wearable GnPs/cellulose strain sensor with a special 2 × 2 double rib knitted fabric structure (KFGS) was prepared by a simple dip-coating method that could be used on a large scale. The KFGS exhibited dual sensing performance with high sensitivity (25.32 kPa−1 at 3 kPa pressure, gauge factor 32.62 at 25% tensile strain), stretchability (e > 25%) and dynamic stability (signal drift < 6% after 300 cycles). Its potential application prospects were also predicted by the monitoring of human movement and physical parameters through a wireless Bluetooth connection.