The biological responses of broomcorn millet root system to manure,N, P and K fertilizer in immature soil were studied on the experimental farm of Shanxi agricultural university with pot culture.The results indicated that N and P fertilization stimulated its root growing,increased its root weight,root number,root length,total and active root absorbing area,and therefore increased the yield of broomcorn millet.The effects of broomcorn millet root growing were not obvious,if only K fertilizer was used.However,combined P,N and K fertilizer with proper rate significantly enhanced the growing of broomcorn millet root.P fertilizer was not only the key factor to get high yield and high quality in immature soil,but also the original active element to soil fertility.The barren soil can be improved rapidly by using P fertilizer.The effect of N,P,K to broomcorn millet root growing was P> N> K.Manure supply can also promote root growing,especially in its earlier growing.The results also showed the strong root promoted soil microbe to multiply rapidly.As a result,the soil enzyme activities of urease and phosphorylase increased.The results of the interactions of root and soil fastened the root and soil system developing towards mature direction.So broomcorn millet yield in immature soil reached the normal level in the very year.