A liquid level sensor based on a single mode-peanut-seven core-peanut-single mode fiber structure is developed. The sensor uses the "peanut structure" as a fiber coupler to improve the coupling efficiency of the single-mode fiber and seven-core fiber. The first fiber "peanut structure" is used to excite the cladding mode, and the second fiber "peanut structure" couples the cladding mode with the core mode to produce interference. Because a phase difference between the cladding and core-based modes appears as they transmit through the seven-core fiber, when the liquid level of the environmental solution changes, the phase difference changes, eventually changing the transmission spectrum. In this study, the liquid level and temperature response characteristics of the sensors with seven-core fiber lengths of 24, 28, and 32 mm were experimentally studied. The experimental results show that with the increase of the liquid level, the transmission spectrum of the sensor shows a blue shift. The liquid level sensitivities of the three sensors are -0.4069, -0.2739, and -0.1653 nm/mm, and their liquid level measurement ranges are 24, 28, and 32 mm, respectively. In the water temperature range of 35?90 ℃, the transmission spectrum of the sensor shows a red shift with an increase in temperature. The temperature sensitivities of the three sensors are 0.0885, 0.0740, and 0.0879 nm/℃. The experiment shows that the sensor has the characteristics of high sensitivity, low cost, and simple fabrication, indicating that it has a good application prospect in the petrochemical industry and other fields.