Abstract: The spatial-temporal variance of soil organic matter was researched in this paper in terms of 300 paddy soil samples in 2004 and 706 paddy soil samples of The Second Soil Survey of China in Hainan Province. The results indicated that the soil organic matter in paddy soil of Hainan Province was decreased during the past 20 years. According to the criterions which was established in The Second Soil Survey of China. The number of regions whose soil organic matter was in the abundance level was decreased from 31.9% to 22.4%. The number of regions whose soil organic matter was in the middle level had changed little, maintaining around 31%. The number of regions whose soil organic matter was in the lack level was increased from 37.3% to 46.6%.The results showed that it was very essential to the preservation of soil fertility with increasing organic fertilizer and straw returned to field.