The southern China is the main producing area of lemon and the deficiency of magnesium in lemon is serious. The resistance to magnesium deficiency of various varieties was different. The variety most resistant to magnesium deficiency was screened out through the comparison of responses of various lemon varieties to low magnesium deficiency. It provideda theoretical basis for the variety layout of lemon planting. In this study，Femminello，No. 1 Yunning Eureka and Tahitilemon，which are the three main varieties of lemons in industrialcultivation，were used as materials and cultivated insands with three concentration treatments including magnesium deficiency(0 g/L)，magnesium insufficiency(6 g/L)，and magnesium normal(24g/L). The physiological responses of various lemon varieties to low magnesium deficiency werepreliminarily revealed through the comparison of plantgrowth，photosynthetic characteristics and magnesium content. Theresults showed that plant growth was inhibited under magnesium stress，however，the response of various varieties wasdifferent. When the magnesium was 0 mg/L，the old leaves of Ferminellao and No.1Yunning showed inverted V -shapedyellowing，but Tahiti did not. Photosynthesis of plants was inhibited under low magnesium stress. Contents of leaf chlorophylldecreased by16.81%，18.01%，13.95%，respectively，in Femminello，No.1 YunningEureka，Tahiti. The transpirationrate，net photosynthetic rate and stomatal conductance of lemons decreased by 9.92%～58.96%，10.70%～37.97%， 9.80%～31.71%. The decreasing amplitude depended on varieties，the photosynthetic physiology order from small tolarge was Tahiti，No.1 YunningEureka，Femminello. Magnesium content in different parts of different lemon varieties alldecreased under low magnesium stress，and the reduction of Femminello，No.1 YunningEureka，Tahiti was22.66%，28.34%，24.32%，respectively. Based on the above indicators，Tahiti was the most resistant variety to low magnesiumdeficiency，No.1 Yunning Eureka and Femminello was not resistant to low magnesium deficiency. Magnesium fertilizer should be supplemented according to different varieties in magnesium deficiency areas.