Agroforestry waste being used as biochar, for agricultural, environmental and climatic applications, has attracted considerable attention, but there are few reports on biochar as electrode modified materials and solid fuel briquettes. In this paper, we demonstrated a new strategy for the mass preparation of micro/nano-powders of biochar with water-dispersibility and their potential applications in different fields. Ultra-fine powders of biochar were easily obtained through pyrolyzing fine powders of smashed biomass waste based on pitch pine at high temperature under oxygen-limited conditions. Micro/nano-powders of biochar were facilely prepared through milling and sieving ultra-fine powders of biochar. Water-dispersible biochars were easily developed through sonicating and centrifugally separating micro/nano-powders of biochar. The structures and properties of two biochar types were characterized, and upper-layer biochar was more steadily dispersed in water and of a smaller size than lower-layer biochar, which was mainly employed as an electrode material in a Pb²⁺ voltammetric sensor and as solid fuel briquettes for pellet biofuels, and other preliminary applications like use as rice bio-fertilizers and Pb²⁺ bio-adsorbents also were given. The satisfactory results indicated that micro/nano-structured and/or water-dispersible biochar will provide promising platforms for electrochemical applications as electrode materials, as a cleaner and renewable alternative to coal fuel, and for other uses, like as bio-fertilizers for crop seedling and growth, and as bio-adsorbents for the removal of hazardous substances.