Avian influenza viruses (AIVs) of the H5, H7, and H10 subtypes pose substantial threats to global public health owing to their high pathogenicity, cross-species transmissibility, and potential to spark epidemics. Rapid and accurate detection is essential for outbreak control and zoonotic risk mitigation. Here, we report the development of a multiplex lateral flow immunoassay (LFA) based on core-shell upconversion nanoparticles (UCNPs) conjugated with subtype-specific monoclonal antibodies targeting the haemagglutinin proteins of H5, H7, and H10 AIVs. The assay achieved limits of detection of 0.0313, 0.0156, and 0.0625 ng/mL for recombinant HA proteins and 2-4, 2-4, and 2-3 haemagglutination units for viral titers of H5, H7, and H10, respectively. No cross-reactivity was observed with other AIV subtypes or respiratory pathogens, and intra- and inter-assay variation remained below 6%, demonstrating high specificity and reproducibility. Validation with 135 avian and 125 human clinical samples showed complete concordance with real-time RT-PCR results. Integration with a smartphone-based analytical platform enabled rapid readout, automated quantification, and cloud-based data sharing, providing results within 10 minutes. This intelligent UCNPs-LFA system combines ultra sensitivity, multiplexing, and field-deployable usability, representing a significant advance over conventional methods. By enabling timely and reliable detection of H5, H7, and H10 AIVs in both animal and human samples, this platform offers a practical tool for early warning, surveillance, and control of emerging zoonotic influenza, thereby contributing to global preparedness against avian influenza outbreaks.