For organic farming, green manure crops such as leguminous forages and barley have been broadly used to improve soil fertility and soil physical and chemical properties by repeatedly cutting and mulching them directly as winter crop in the field in the rotation. In this investigation we selected 78 agricultural farm corporations as well as individual organic farmhouses related to crop rotation from greenmanure crops to main crops in order to analyze the relationship of cropping system between main crops and green manure crops. The results showed that the green manure crops were divided into two groups as leguminous and nonleguminous crops, representing that those are limited to specific climate and farming systems of regions. Also the 10 or less green manure crops including sudangrass, hairyvetch, italian ryegrass, sorghun, buckwheat, oat, pea, rye, clover, and canola which belong to leguminous crops which are presently cultivated from the organic farmhouses within the rotational crop system. We also confirmed that the major main crops are sweet potato, soybean, corn, tobacco, spinach from usage frequency analyzed by NetMiner H 2.6 which was used to estimate the rotational cropping system among the green manure crops and main crops.