Legitimate communicating parties can leverage the randomness of wireless channel state to extract shared key sequences that are information-theoretically secure. To enhance the efficiency of wireless channel key extraction， a difference-based shared key extraction scheme via multi-level quantization was proposed. In the scheme， random modulation was employed to perform high-frequency sampling of the wireless channel， and two quantization algorithms integrated with random sampling difference — Adaptive Symbol Quantization （ASQ） and Balanced Multi-bit Modified Quantization （BMMQ） — were introduced to process the first-order differential sequence， so as to obtain the original key sequence. On this basis， an information negotiation algorithm was applied to correct inconsistent bits in the original key， and the signal was reconstructed using the original key and the first-order differential sequence， and then the signal was requantized， ultimately achieving key synchronization between legitimate communicating parties. Experimental results demonstrate that random sampling difference reduces the correlation coefficient between adjacent sample points to below e?1， thereby decreasing statistical dependence in the key sequence effectively； under a Signal-to-Noise Ratio （SNR） of 25 dB， the ASQ algorithm reduces the Key Disagreement Rate （KDR） to 3.8×10?? while maintaining an Original Key Extraction Rate （OKER） of 0.86； under lossless quantization conditions， the BMMQ algorithm reduces the KDR to 7×10?3. The finally generated shared key sequences pass the NIST （National Institute of Standards and Technology） randomness test， validating the security and effectiveness of the keys.