Abstract: Taking the soil of Eucalyptus plantation in the red soil area of southern Guangxi as the research object, 15 indexes of the soil of generations 1, 2, 3 and 4 were measured by the method of space replacing time. The soil fertility quality of Eucalyptus plantation of different generations was evaluated by means of significance comparative analysis and 3 comprehensive index evaluation methods(fuzzy mathematics method, Nemero index method and grey correlation analysis method), Finally, the regression verification is carried out. These results indicated that the soil pH value decreased after several generations of continuous planting. Forest Ⅳ 4.41 was lower than forest Ⅰ 4.71, showing a certain acidification trend, and the contents of organic matter, available phosphorus and zinc also decreased; the evaluation results of Nemero index method and fuzzy mathematics method are consistent, while the evaluation results of grey correlation analysis method are inconsistent with the first 2 methods; further through the regression verification, it is found that the comprehensive evaluation results of Nemero index method and fuzzy mathematics method are in line with the actual production situation, while the results reflected by grey correlation analysis method are distorted. The change of soil fertility quality after continuous planting: II>I>III>IV, soil fertility began to decline from forest III, and it is necessary to supplement the missing nutrients in time to maintain the stability of soil fertility quality.