In the process of ultra long span fiber frequency transmission, factors such as power attenuation and additional noise of active devices lead to weak frequency signal at the receiving end, which limits the signal detection resolution and sensitivity. To solve this problem, the research team proposed a dual-mixing time-delay detection of weak frequency signals enabled by local-oscillator optical enhancement. The weak carrier signal power was enhanced by a coherent laser, and the dual-mixing time-delay detection structure was used to improve the receiving sensitivity. At the same time, the high signal-to-noise ratio signal extraction was realized by combining with the balanced detection technology. The experimental results show that compared with the traditional intensity modulation / direct detection method, the dual-mixing time-delay detection of weak frequency signals enabled by local-oscillator optical enhancement can effectively improve the sensitivity of the receiver by about 10 dB, the RF power is increased by 25 dB under the same input power condition, and this method achieves excellent frequency stability, with Allen deviation of 2 × 10^-13@1 s and 2.1 × 10^-15@10 000 s, and stability of 3 × 10^-17@1 s and 3 × 10^-19@10 000 s under the condition of difference frequency of 10 kHz, which verifies the feasibility and significant advantages of the proposed method in high-precision optical fiber frequency transmission.