【Objective】Soil organic matter (SOM) is an important index for evaluating soil fertility and soil carbon pools. SOM usually has strong spatial and temporal variability for the complicated soil forming process and human activity. Studying the temporal and spatial variability of SOM could provide an important reference for the adjustment of agricultural planting structure and response to global climate change.【Method】The contents of SOM of 0-20 cm soil layer in Hainan Island in 1980s and 2012 were collected and measured by field investigation and soil sampling. RandomForest (RF) model was used to predict spatial distribution of SOM based on the training set of 410 and 128 samples, and then the predictions were validated with validating set of 103 and 32 samples, respectively. Then the spatial and temporal variability and driving factors of different land use types in Hainan Island in resent thirty years were studied by using statistical method combined agricultural statistical data.【Result】The mean value of SOM contents in 1980s was 20.57 g·kg~(-1), showing a distribution that SOM contents gradually decreased from southwest to northeast parts of the island. And SOM contents were mainly in two levels of 15-20 and 20-30 g·kg~(-1), which occupied 75.29% area of the whole island. The mean value of SOM contents in 2012 was 15.89 g·kg~(-1), showing a distribution that SOM contents were higher in the southwest and northeast parts, lower in the west and south parts. And the contents of SOM were mainly in two levels of 10-15 and 15-20 g·kg~(-1), which occupied 78.28% area of the whole island, but the ratio of 15-20 and 20-30 g·kg~(-1) levels was 66.04%, which lowered 9.45 percentage points compared with 1980s. The order of SOM contents in different land use types was: paddy field > garden plot > dry land. And there was a significant difference in SOM contents among three land use types in 1980s. In 2012, there was a significant difference in SOM contents between paddy fields and dry land, dry land and garden plot, while the difference in SOM contents between paddy fields and garden plot was not significant. 【Conclusion】 After nearly 30 years, SOM contents of Hainan Island showed a decreasing trend overall. In 2012, the mean value of SOM contents decreased by 4.68 g·kg~(-1) compared with 1980s, with a reduction of 22.75%. The mean value of SOM contents of paddy field decreased by 6.42 g·kg~(-1), with a reduction of 27.34%, which was most obvious among three land use types. And the mean value of SOM contents of garden plot decreased by 2.65 g·kg~(-1), with a reduction of 14.25%, while the mean value of SOM contents of dry land decreased by 1.28 g·kg~(-1), with a reduction of 8.84%. Rice crop rotation, land reclamation and increasing multiple crop indexes were the main reasons that caused the decrease of SOM contents in Hainan Island.