In this paper, the effects of coexisting high potassium (K) and high aluminum (Al) on magnesium (Mg) leaching of different Mg fertilizers in latosol derived from the shallow sediments in Hainan was studied in order to provide a theoretical basis for the rational application of Mg fertilizers. Latosol derived from shallow sediments was collected and four treatments were designed, including non K and Al(–K–Al), high K (+K), Al toxicity (+Al), and coexistence of high K and high Al (+K+Al), and then the leaching characteristics of five Mg fertilizers, including magesium sulfate monohydrate(MgSO₄·H₂O), dolomite (CaMg(CO₃)₂), Mg(OH)₂, MgO, calcium magnesium phosphate fertilizer (CaMgP) were studied through simulated soil column experiments. The results showed that Mg concentration in the first leachate was the highest (125.47–898.81 mg/L), steeply decreased in the second and third leachates (8.79–157.64 mg/L and 0.51–29.28 mg/L, respectively), then tended to stable in the following leachates (0.25–9.41 mg/L). Mg concentrations in the leachates treated with Mg fertilizers were higher than that of CK, with MgSO₄·H₂O being the highest (898.81 mg/L) and CaMg(CO₃)₂ the lowest (212.50 mg/L). Mg concentrations in the leachates under +K+Al were significantly higher than those of other treatments, and the accumulated contents of leached Mg under different types of Mg fertilizers ranged from 19.16–142.96 mg, and were almost always in the order of +K+Al > +Al > +K > –K–Al. The accumulated contents of leached Mg under +K+Al treatment were in the order of MgSO₄·H₂O>CaMgP>(Mg(OH)₂> MgO>CaMg(CO₃)₂, with the lowest being CaMg(CO₃)₂ (8.22%) and the highest being MgSO₄·H₂O (82.54%). After 11 times leaching, compared with CK, in the 0–20 cm soil layer, except for MgSO₄·H₂O, Mg fertilizers increased soil pH, and soil exchangeable Mg contents were almost all in the order of+K+Al < +Al < +K < –K–Al. Under the same treatment, there was almost no significant difference in exchangeable Mg content between CK, MgSO₄·H₂O, and CaMg(CO₃)₂ treatments, but both were significantly lower than Mg(OH)₂, MgO and CaMgP. Therefore, attention should be paid to water management after Mg fertilizer application to prevent excessive Mg leaching. +Al has a greater impact on Mg leaching than +K, and +K+Al can promote Mg leaching, then, MgSO₄·H₂O, prone to leaching, should not be used as a base fertilizer, especially under the coexistence of K and Al, it should be applied in small amount and multiple times. Comparatively, CaMg(CO₃)₂ with a low Mg leaching is recommended as the base fertilizer.