With the continuous development of soilless cultivation technology in China, the testing of the internal components of hydroponic nutrient solutions, which are a key part of soilless cultivation technology, has become a hot topic of research. Magnesium ions (Mg 2+) are essential nutrients for important physiological processes such as photosynthesis, respiration, and the synthesis of genetic material in plants, so the accurate detection of Mg 2+ content in soilless nutrient solutions is of key significance for the regulation of crop production. A summary of the available literature showed that Mg 2+ detection had evolved from traditional atomic absorption to current fluorescent probe detection techniques, but Mg 2+ fluorescent probe materials were complex to synthesize and were susceptible to interference from calcium (Ca 2+) and zinc (Zn 2+). Salicylaldehyde, a readily available and inexpensive intermediate for commercial fine chemical synthesis, can be combined with Mg 2+ to form a stable chelate for Mg 2+ detection. A salicylaldehyde fluorescent probe combined with a microfiber optic spectrometer was used for the detection of Mg 2+ in nutrient solutions to investigate the detection mechanism. The sensitivity, selectivity, and interference resistance of the molecular probe were systematically determined, and the reproducibility of the salicylaldehyde fluorescent probe was investigated through the measurement and spiked recovery of strawberry nutrient solutions. Experimental results showed that the fluorescent probe binded to the magnesium ion to form a stable complex, producing chelated fluorescence enhancement. The fluorescence response intensity of the salicylaldehyde probe was well linear in the concentration range of 0~800μmol/L Mg 2+, with a correlation coefficient of 0.999 and a response time of about 2min, enabling the rapid determination of Mg 2+ in solution. The probe showed good selectivity for Mg 2+, with the fluorescence response intensity of equal concentrations of Ca 2+ and Zn 2+ ions increasing by only 2.5% and 9.1% of the Mg 2+ intensity year-on-year, with a weak fluorescence enhancement compared to the blank group. At the same time, the probe had good resistance to interference, and the fluorescence intensity measured by solutions of Mg 2+ coexisting with Ca 2+ and Zn 2+ coexisting with Mg 2+ in equal amounts had a year-on-year growth rate between -0.004 and 0.009 compared with the fluorescence intensity measured by a single Mg 2+ solution salicylaldehyde fluorescent probe, with the growth rate fluctuating up and down by less than 0.01. The five solutions of Ba 2+, Cu 2+, Mn 2+, Fe 2+, and Fe 3+ showed fluorescence intensity growth rates ranging from -0.21 to -0.91 year-on-year, with a fluorescence burst compared with the pure water blank group. The spiked recoveries of the actual samples ranged from 99% to 104.9% with a relative error of less than 1.33% and an RMSE of 5.78μmol/L, demonstrating the good sensitivity and reproducibility of the salicylaldehyde fluorescent molecular probe for the determination of Mg 2+ concentrations in nutrient solutions. In conclusion, the research result initially validated the feasibility of salicylaldehyde fluorescent probes for Mg 2+ detection in nutrient solutions.