Abstract: In the replant of apple orchard, some diseases often break out in young apple trees. Applying organic ferment fluid with proper ratio of certain organic materials(Patent No. ZL 2009 1 001 5530.2) was proved effective to alleviate these diseases. Using pot experiment and the Fuji apple seedlings grafted on Malus robusta biennial as the test materials, six concentrations of the fermented organic fluid were designed to irrigate the seedlings: CK(distilled water), 1%(T1), 3%(T2), 5%(T3), 7%(T4) and 9%(T5). Each treatment had three replicates and each pot had three irrigations. The effect of different adding levels on the young apple tree biomass and soil properties in continuous apple cropping soil were studied. The results show that: 1) In spring, summer and autumn, all the five irrigation concentrations of fermented organic fluid could improve the soil organic matter, ammonium nitrogen, nitrate nitrogen, available phosphorus and potassium contents of the pot soils to some extent, and the maximum increase was with T5. 2) The fermented organic fluid has the effect of promotion in low and inhibition in high concentration. When irrigating levels were lower than 3%(T3), there is positive effect but negative when the adding levels higher than 5%. The irrigating level of 3%(T2) gave the highest biomass and the most satisfactory disease alleviating effect. 3) Irrigating young apple trees with the five fermented organic fluid concentrations could increase the activities of soil urease, catalase, invertase and neutral phosphatase. The 3% treatment(T2) gave the highest activities. 4) Applying the fermented organic fluid could enhance the microorganisms quantity significantly. The increase was in order of bacteria higher than fungi and higher than actinobacteria.