Frequency transfer is a key technology that supports long-distance frequency comparison, and its performance directly affects the establishment of a global unified timescale, the interconnection of optical atomic clock networks, and the further development of quantum metrology systems. To address the limitations in resolution and sensitivity at the receiver side caused by power attenuation during ultra-long-haul fiber frequency transfer and the additional noise introduced by active components, this paper proposes a weak frequency signal detection scheme enhanced by local oscillator light. The scheme employs a coherent laser to amplify the power of the weak carrier signal, utilizes a dual heterodyne delay detection structure to improve sensitivity, and integrates a balanced photodetector for high signal-to-noise ratio (SNR) extraction. Compared with conventional intensity modulation/direct detection (IM/DD) methods, the proposed approach improves the receiver sensitivity by approximately 10 dB, the RF power is increased by 25 dB under the same input optical power conditions. Experimental results demonstrate that the system achieves Allan deviations of 2×10-13 @1 s and 2.1×10-15 @10000 s, verifying that the local-oscillator-enhanced detection method achieves a receiver sensitivity of -49 dBm. Meanwhile, the constructed dual-mixing time-delay detection system achieves a stability of 3×10-17 @1 s and 3×10-19 @10,000 s under a beat frequency of 10 kHz, demonstrating its feasibility and significant advantages in high-precision optical frequency transfer.