Aiming at the medium-and low-grade lithium clay with L₂O<2.0%（mass fraction） in Yifeng zone,Jiangxi province,the technical route of extracting lithium carbonate by ammonium sulfate process was studied.First,two-step roasting process was selected,which was beneficial to defluorination,improvement of the lithium leaching rate,and prevention of the occurrence of kilns.In the process of removing impurities in leachate,a large amount of dissolved aluminum ions were converted into the useful alum salts such as KAl（SO₄）₂·12H₂O and NH₄Al（SO₄）₂·12H₂O. Compared with traditional gypsum method,a large amount of solid waste was avoided.By this process,70% Al ions were converted into alum salt crystals,while bringing out a large amount of crystallization water,reducing subsequent concentration pressure.The advantage is obvious in comparison with traditional gypsum method with production of a large amount of solid waste.The analysis results of XRD and Li₂O content of the carbonization product showed that the purity of lithium carbonate was over 99%,and the lithium yield was 50%~60% in whole process.In comparison,the same process was used to lepidolite from Yichun 414 mine with 4.0% Li₂O content.Due to the lower aluminum content in 414 mine,the obtained Li ion concentration in the leachate under the same impurity removal difficulty was higher,the concentration ratio was smaller,and the recovery rate from Yichun 414 mine was higher.The experimental results showed that,aiming at of extracting lithium carbonate from medium-and low-grade lithium clay,by appropriately changing parameters,this process can be applied to lithium extraction from high lithium content with lower difficulty.