This Mobile visible light communication (VLC) systems, embedding light emitting diodes (LEDs) into unmanned aerial vehicles (UAVs) to simultaneously achieve lighting and high-speed communication, have received widespread attention. Due to the mobility of UAVs, the line-of-sight link between transceivers is not always maintained. Therefore, intelligent reflective surfaces (IRSs) can be introduced to dynamically establish links. However, the broadcast characteristic of optical wireless links makes transmission vulnerable to information leakage. We investigate the physical-layer security of an IRS-UAV-aided mobile VLC system and utilize downlink non-orthogonal multiple access (NOMA) to support security access for multiple terminals. The secrecy sum rate (SSR) maximization problem is formulated with jointly optimizing UAV position, IRS allocation matrices and NOMA allocation power. Alternating optimization algorithm is used to tackle the nonlinear mixed integer non-convex problem. Numerical results indicate the proposed security scheme greatly outperforms the other four benchmark schemes in terms of SSR, and the application of NOMA effectively improve the security performance.