NOVELTY - Method for preventing or controlling soil nematodes using filtrate of fermented compost, involves isolating Bacillus thuringiensis from fresh compost sample, culturing isolated strain and preparing fermented liquid, filtering fermented liquid, diluting filtrate, adding lawn soil in a plastic basin, adding diluted filtrate containing B.thuringiensis into the soil, uniformly spreading tall fescue seeds into plastic basin, planting at room temperature and isolating and identifying the number and type of soil nematodes.    USE - The method is useful for preventing or controlling soil nematodes by using filtrate of fermented compost comprising B.thuringiensis, and also useful for inhibiting growth of plant parasitic nematodes, changing community composition of soil nematodes, enhancing stress resistance of lawn plants and promoting growth of lawn plants, preferably tall fescue grass.    DETAILED DESCRIPTION - Method for preventing or controlling soil nematodes by using filtrate of fermented compost, involves (a) isolating Bacillus thuringiensis by weighing fresh compost sample (10 g) and adding same in triangular flask comprising sterile water (90 ml) and glass balls (20 pieces), shaking and completely and evenly dispersing microorganisms in the sample in the liquid, transferring 1 ml of the liquid into bottle, adding the mixture in boiling tube filled with 9 ml of sterile water and mixing evenly to obtain diluted solution having concentration of 10-1, diluting the solution to obtain diluted liquids having concentration of 10-2, 10-3, 10-4, 10-5 and 10-6, transferring 0.1 ml of each diluted solution in whole beef extract-peptone solid medium and evenly mixing, reversely locating flat plate including the solid medium in constant temperature culture box and culturing for 1 day at 37 degrees C, (b) preparing B.thuringiensis fermented liquid by purifying the isolated B.thuringiensis strain for 2 generations and adding same to 250 ml of triangular flask filled with 50 ml of beef extract-peptone solid medium and culturing at 37 degrees C and 180 revolutions per minute (rpm), performing turbidimetric detection at 600 nm wavelength, drawing growth curve of the microorganism by taking optical density value of the suspension liquid as the vertical coordinate and the culturing time as the transverse coordinate, obtaining the time that the B.thuringiensis strain grows to the stable stage according to the growth curve, purifying the B.thuringiensis strain, adding same in 250 ml of triangular flask filled with 50 ml of liquid medium and culturing for 8-12 hours at 37 degrees C and 180 rpm, taking the strain at stable stage and counting viable count in each ml of liquid by direct microscopic method, and filtering the liquid at stable stage using microfiltration membrane having pore size of 0.22 microns to obtain filtrate, (c) diluting the B.thuringiensis fermented liquid, taking some part of the filtrate and diluting the filtrate for 4 times and 8 times, (d) taking plastic basin having height of 14 cm and diameter of 20 cm as container for building lawn building system, adding 25 kg of lawn soil in basin and planting 3 g of tall fescue seed, adding 10 ml of diluted B.thuringiensis fermentation liquid filtrate in the basin when the plant in the lawn grows to 5 cm for preventing and controlling soil nematodes, isolating and identifying the number and type of soil nematodes after 75 days, identifying the diversity, purifying and further culturing for two generations, where first generation of culture is carried out by inoculating the strain to number 1 flat plate solid medium and reversely locating the culture dish in constant temperature culture box at 37 degrees C and culturing for 1 day, isolating the bacterial colony from the purified first generation strain and repeating the process.