Magnesium (Mg) ions play a crucial role in the growth and development of tea plants (Camellia sinensis). In this study, the ion kinetic method was used to analyze the effect of ions from various elements on the Mg ion uptake rate in two tea plant varieties (Rougui and Shuixian). Additionally, Mg ion content and the expression intensity of CsMGT5 gene in the tea plant’s root system were measured to further understand how different elemental ions affect Mg ion uptake and accumulation. The results revealed that while the trends in the effects of different elements on Mg ion uptake were similar in both Rougui and Shuixian roots, the magnitude of these effects was lower in Rougui and higher in Shuixian. In the presence of only Mg ions in the solution, the tea plant’s root system exhibited the highest intensity of CsMGT5 gene expression, the fastest uptake rate of Mg ion, and the highest Mg content. Conversely, the presence of nitrogen, phosphorus, and potassium ions alone reduced CsMGT5 gene expression, Mg ion uptake rate, and Mg content in the tea plant’s root system. However, differences in the impact of these three elements on Mg ion uptake and accumulation were not statistically significant. In addition, with the increase in the types of added ions, the Mg ion uptake rate by tea plants gradually declined, indicating a decreasing demand, with Mg accumulation showing a downward trend. Statistical analysis of correlations showed that CsMGT5 gene expression in the tea plant’s root system positively regulated the maximum uptake rate of Mg ion (I_max value, 0.94 **). The I_max value negatively regulated Mg ion content in solution (C_min value, −0.94 **), and the C_min value negatively regulated Mg ion content in the tea plant’s root system (−0.95 **). In conclusion, the presence of different elemental ions significantly influenced the uptake and accumulation of Mg ions in tea plants, with the magnitude of this effect intensifying as the number of elemental types increased. A positive correlation was observed between the capacity for Mg ion uptake and accumulation capacity in the tea plant’s root system and the expression intensity of the CsMGT5 gene within the root system. This study offers valuable insights and serves as an important reference for leveraging Mg to regulate tea plant growth in practical agricultural applications.