Soil magnesium(Mg)deficiency has increasingly become an important factor restricting the production of citrus in China.Excess potassium(K)in soil can further reduce the absorption and transport of Mg in roots through K-Mg antagonism，which in turn leads to insufficient Mg in the shoots and affects growth.Therefore，two K levels of high K(300 mg·kg-1)，suitable K(150 mg·kg-1)and five fertilizer K/Mg ratios(K/Mg，4∶0，4∶1，4∶2，4∶3，4∶4)were set up under pot simulation conditions，and the differences of growth and nutrient uptake between two typical citrus rootstocks named Xiangcheng(Citrus junos Sieb.ex Tanaka)and Zhi [Poncirus.trifoliata(L.)Raf.]，were studied under the above conditions，in order to provide the basis for clarifying the suitable soil K/Mg ratio and balanced fertilization.Compared with optimize K treatment，the plant heights of Xiangcheng and Zhi under high K treatment were decreased by 7.7～11.7 cm；the biomass，accumulation of K and Mg in citrus shoot and root were also declined.When fertilizer K/Mg ratio was decreased from 4∶0 to 4∶4，the soil exchangeable Mg was increased from 61 to 166 mg·kg-1，the leaf Mg concentration was increased from 1.09 to 4.14 g·kg-1，and the biomass was increased first and then decreased.Regression equations showed that the averaged biomass and the dry weight of each part were the highest when the fertilizer K/Mg ranged between 4∶1 and 4∶2.While excessive Mg application resulted in decreased soil K/Mg ratio and shoot K/Mg ratio，thereby inhibiting the growth of citrus rootstocks.Under high K and optimize K treatments，the Mg concentration in Zhi root/shoot part was significantly lower than that of xiangcheng.Applying high K on acidic Mg-deficient soil will aggravate the symptoms of Mg deficiency in citrus.Maintaining the soil K/Mg ratio between 1.5 and 2.0 is conducive to citrus growth.Compared with Xiangcheng，Zhi is more tolerant to Mg deficiency by translocating more Mg to the shoot.In conclusion，on the basis of rational application of K fertilizer，paying attention to the balanced application of K and Mg and selecting suitable rootstock varieties can alleviate the problem of Mg deficiency in citrus production.