This study was carried out to investigate the effect of legume cover crop culture on earthworm fauna in organic farmland. We compared sod culture with two kinds of legume crops of hairy vetch and crimson clover on organic citrus orchard to natural sod culture and conventional orchards in Jeju Island. We analyzed the soil characteristics and investigated the density of earthworms from the orchards. Organic matter content did not show much difference in soil analysis between organic and conventional orchard. But the biomass of earthworms in organic orchards is 3.8 times to 7.0 times higher than that in conventional cultivated orchards, and individuals of earthworms on organic orchards were 2.3~18 times higher than conventional orchards. The biomass of earthworms on hairy vetch and crimson clover cultivation was 44.8 g, 47.2 g in 2016, and 78.7 g, 31.8 g in 2017, respectively, which were higher than 32.8 g and 9.5 g of those on natural sod cultivation. Through this study, we found that hairy vetch and crimson clover cultivation improve the earthworm occurrence density in the soil on organic citrus orchard.