The phosphorus (P) changes in soil, dominant plant (Haloxylon ammodendron) and main insect (Julodis varioloris Pall) in desert area of Sinkiang were periodically measured, and the P transference between soil, plant and insect was investigated. The results shows that Carbon/phosphorus (C/P) in Haloxylon ammodendron leaves negatively correlated with available phosphorus in soil. The P and RNA content in Julodis varioloris Pall negatively correlated with C/P in Haloxylon ammodendron leaves, while positively correlated with available phosphorus in soil. This indicates that the P and RNA in Julodis varioloris Pall were directly affected by C/P in Haloxylon ammodendron leaves, and indirectly affected by available phosphorus in soil. The P dynamics between soil and plant may be an important factor that drive Julodis population change. The population of Julodis varioloris Pall was consistent with the changes of the P and RNA contents in natural environment. It demonstrates that the dynamic change of Julodis population in desert area can be estimated by the changes of the P and RNA contents. This gives us a new way to study insect population in microcosm.