A long-term (over 10 year) fertilization experiment on the double rice cropping system was conducted in three types of hydragric paddy soils in Guilin, Qinzhou and Yulin of Guangxi, South China to investigate variation of crop grain yield and soil fertility with time and differences between the three experimental sites in contribution of the major fertility factors to crop yield and relationship between the two using path analysis, The experiment was designed to have two treatments, CK (no fertilizer) and F (conventional fertilization). Results show that under Treatment CK, grain yield varied in the range of 666~846 kg hm^-2, showing a significant decreasing trend with time at the site of Guilin where the basic soil fertility is rather low, but it was relatively stable, varying in the range of 3 500~4 577 kg hm^-2, at the sites of Yulin and Qinzhou where the basic soil fertility is relatively high. However, under Treatment F it increased by 522% over that in Treatment CK, showing a significant rising trend at the site of Guilin, but at the sites of Yulin and Qinzhou, it did only by 20%~67%. Soil fertility in Treatments F remained almost unchanged or increased to a varying extent. For instance, soil available P increased sharply to a significant extent at the sites of Guilin and Qinzhou where its initial value was lower than 10 mg kg^-1, but it did not change much at the site of Yulin where its initial value was 50 mg kg^-1. Soil organic matter and total nitrogen content also varied from site to site. Soil organic matter displayed a rising trend and TN content was high (>3 g kg^-1) at the site of Guilin where the temperature is lower, while at the sites of Yulin and Qinzhou where the temperature is higher, the former displayed a declining trend and the latter was relatively low (1~2.5 g kg^-1), showing differences between the sites in accumulation and release of soil organic matter. Differences between the sites in major fertility factor contributing rice yield were also observed. Soil available phosphorus is the primary factor at the site of Guilin while at the sites of Yulin and Qinzhou, soil organic matter and total nitrogen are. Therefore, taking proper measures in light of the soil properties of a region is a guarantee of sustainable effective soil building.