In the quantum noise stream cipher (QNSC) system, the low-order plaintext is encrypted by pre-shared keys into high-order ciphertext. However, high-speed optical communication systems have a huge demand for pre-shared keys. On the other hand, the separation of the secure communications sub-system from the secure key distribution (SKD) sub-system increases potential security risks and introduces additional resources overhead. In this letter, we propose an artificial amplitude noise-based SKD scheme (AAN-SKD) in QAM/QNSC to generate secret key for legal parties accordingly. The two orthogonal PAM symbols are superimposed to generate QAM symbols. Thus, the AAN-SKD can also be implemented in PAM modulation. In addition, the data transmission and AAN-SKD are completed in the same channel. Experimental results indicate that the key generation rate and key consistency ratio of the proposed scheme can reach 188.22 Mbit/s and 91%, respectively. Compared with quantum key distribution, the AAN-SKD has the advantage of lower cost, better compatibility, and a higher key rate.