At present，the basic production process route of West Taijinar Salt Lake is that brine is naturally concentrated by evaporation in the salt field，and potassium and lithium products are produced by using potassium mixed salt，carnallite and residual lithium-rich old brine in the later stage of evaporation，but the yield is not high.The loss of potassium and lithium in the evaporation process of West Taijinar Salt Lake brine was compared and studied by on-site solid-liquid phase sampling observation and simulated evaporation experiment.The results showed that the potassium in the brine was enriched to more than 20 g/L，and the potassium mixed salt ore began to precipitate.Lithium was continuously enriched in this process，from 0.19 g/L to 2.12 g/L.The evaporation experiment results were basically in line with the actual production of the salt field.According to the experimental results，the loss of potassium and lithium in different stages of salt field was estimated.The loss rate of potassium in sodium salt field was about 12.3%，and the total recovery rate of potassium in potassium salt field was 84.4%.The loss rate of lithium was about 6.50% in the sodium salt stage，11.59% in the potassium mixed salt stage，6.21% in the carnallite stage，and 6.44% in the old brine stage.The total loss rate in the salt field system was about 30.74%，and the lithium loss in the potassium salt crystallization stage was the largest.