•The proposed scheme is practical and compatible, which does not require extra dynamic parameters and physical devices.•Compared with existing SKGD schemes, the proposed proposal has higher key generation rate or longer key distribution distance.•When the agreement data is placed at the 7th bit of the symbol, the highest bit can be used for transmission, so that the key distribution and secure transmission can be integrated.•The key generated by the proposed scheme has true randomness and no relationship with the pre-shared information.•The randomness of noise, quantum stream cipher, and added Gaussian white noise at receivers collectively ensure the security of the proposed scheme.•Seed keys can be generated continuously by sharing a small amount of information only once. Considering the key demand in the secure optical fiber communication, a key generation and distribution scheme based on random noise variances is proposed. The noise of optical communication systems is inevitable due to the influence of various factors. The additive noise that cannot be eliminated is random after digital signal processing, which ensures the randomness of the key. However, the range of system noise variances is small and the noise of links is exposed. A random Gaussian white noise is added at receivers, which increases the noise fluctuation and enhances security. Legitimate parties obtain secure keys by calculating the data inconsistency rate, where the consistency comes from the correlation of noise variances in adjacent time slots over a period of time. Experimental results demonstrate that the error-free key is obtained with the key generation rate of 1.6 Mbit/s over 105 km standard single-mode fiber. Moreover, the security analysis shows that the proposed key generation and distribution scheme can resist fiber-tapping attacks.