In this work, the intelligent reconfigurable surface (IRS) has been proposed to relax the requirement of line-of-sight (LOS) channel gain of the cell-edge user in the non-orthogonal multiple access visible light communication (NOMA-VLC) system, in which the physical layer security (PLS) of the cell-edge user has been enhanced by optimizing the power allocation method at the transmitter. Besides, different mobility models have been adopted for the paired NOMA users to cope with the real indoor environment. The optimal power allocation method and non-silent probability (NSP) of the transmitter are mathematically derived by considering different cases of users’ channel gains. Through simulations, performances of the secrecy rate of the cell-edge legitimate user and NSP of the transmitter are analyzed in detail, where the impacts of the main system parameters are also studied. This work can serve as a good reference for further study of the secure VLC system.