The present invention discloses a micro-nano level dye for marking sentinel lymph nodes and its preparation method and application. The invention connects the dye used to mark the lymph nodes to polymer nanoparticles or microparticles through any one or more methods such as adsorption, embedding, or chemical bonding, transforming the small molecule level dye into nano-scale and micro-scale dyes. The polymer nanoparticles or microparticles with the attached dye are then used to mark and identify sentinel lymph nodes. The provided dye connected by polymers formed from nanoparticles or microparticles can take advantage of the steric hindrance effect of the spatial volume of the polymer nanoparticles or microparticles and the affinity of the polymer to lymphatic vessels, allowing the dye to be retained by the sentinel lymph nodes or to slow down its flow through them. This can become a new type of tracer material for tumor sentinel lymph node biopsy, with broad clinical application prospects.