Abstract: Using Nanfeng tangerine yard as research subject，the variation of microorganism category，enzyme activities，soil nutrient and fruit quality were studied under different conditions such as 2 years grass，4 years grass，8 years grass and clean cultivation. The bacteria quantity in the soil of Nanfeng tangerine yard，ranked first，account for 90% of total microorganisms. Most detected soil microorganism quantity and soil enzyme activities，except phosphomonoesterase，were increased under sod culture treatment，compared to clean tillage. Natural grass can increase the organic matter and the content of TN，TP，TK in the soil，compared with the control，the soil organic matter and the content of TN，TP，TK in 8 years natural grassland increased separately by 196.4%，56.53%，66.67% and 77.08%. The contents of alkali-hydrolyzable N，available P，and available K in soil with grass 2 years weresignificantly lower than that of the control while increased by 25.98%，3.1%，90.57% in soil with grass 8 years. The naturally grown grass significantly increased the soluble solids and soluble sugar of Nanfeng tangerine. Correlation analysis indicated that soil microorganism，soil enzyme activities and soil nutrient mostly showed very significant correlation each other under different culture models. Naturally grown grass could improve effectively the soil microorganism quantity，soil enzyme activities，soil fertility and enhanced fruit fresh eating quality.

Key words: citrus, yard, natural grass, soil microbiological characteristic, soil nutrient, soil enzyme activity, fruit quality