Purpose: This study aimed to establish a ratiometric electrochemical mixed aptamers sensor based on catalytic hairpin assembly (CHA) for sensitive， accurate， and stable detection of tetracycline (TC). Method: This method improveed recognition ability by capturing the same target through two mixed aptamers. Realize enzyme free signal amplification of the target through CHA reaction， using ferrocene (Fc) and methylene blue (MB)， which were easily distinguishable from peak values， as signal switch molecules， labeled on DNA probes to generate proportional electrochemical response signals. Result: The linear range of TC detection by this sensor was from 50 fg/mL to 100 ng/mL， which was wider than the linear range of two single aptamer based sensors. The limit of detection (LOD) was 77 fg/mL， which was 8.6 times and 6.1 times lower than the LOD of two single aptamer based sensors， respectively. This sensor had specificity for TC， with a relative standard deviation (RSD) of 4.2% in repeatability evaluation. After 9 days of storage， the signal response of the constructed sensor could still maintain at 92% of the initial value， and it had been successfully used for the detection of TC in milk. The actual sample detection results had a spiked recovery rate (87.1%-107.2%) that was consistent with high performance liquid chromatography (HPLC) (92.1%-100.4%). Conclusion: The ratiometric electrochemical mixed aptamers sensor constructed in this study could be used for sensitive detection of TC in milk， and this method could provide reference for the detection of various antibiotics.