In an optical camera communication (OCC) system, multi-level modulation is essential for data rate enhancement with the finite frame rate of the receiving camera constraint, where the K-means algorithm is widely used as a thresholding scheme. The result of K-means clustering is sensitive to initial cluster centers. In this paper, we propose a multi-level modulation scheme utilizing the pilot-aided K-means (PAK) algorithm. PAK algorithm innovates in both obtaining the state of the stripes propagated through the optical channel under different environments and overcoming the susceptibility of K-means. Our scheme could prompt data rate and improve the performance of OCC. Finally, non-orthogonal multiple access (NOMA) pattern is designed based on the proposed scheme to achieve multiplex communications.