Salinity gradient power harvesting utilizes the chemical potential energy difference between seawater and freshwater or solutions with varying salt concentrations. This energy can be efficiently converted into electricity via reverse electrodialysis on ion-selective membranes. However, current ion-selective membranes face challenges such as low mechanical strength, poor ion selectivity, and ion permeability. The development of high-performance ion-selective membranes is crucial for advancing the industrial application of salinity gradient energy conversion technology and expanding its scope. Sulfonated poly(ether ether ketone) (SPEEK) has garnered attention because of its rich surface charge and excellent mechanical properties. However, its relatively low output power density limits its potential. This thesis optimizes the interaction between SPEEK and other polymers and porous nanomaterials to construct composite membranes with high mechanical properties, high stability, improved ion selectivity, and permeability, enabling more efficient energy conversion.