A survey of weed communities in the lemon orchard in Ruili city, Yunnan province, was conducted to compare the differences in weed communities between covered and open lemon gardens. The result showed that18 species of weeds belonging to 9 families and 9 orders were found in the lemon orchard RG (plastic film mulching, no herbicide), 23 species of weeds belonging to8 families and 8 orders were found in lemon orchard RH(open field planting, using herbicides 5 times a year) and 23 species of weeds belonging to 9 families and 9 orders were found in lemon orchard RI (plastic film mulching, using herbicides 3 times a year). There was no significant difference in the species richness of weeds while there were significant differences in weed density in the 3 types of lemon orchards; and the weed density in the RH plots was significantly higher than that in the RG and RI plots. Imperata cylindrical, Cynodon dactylon, Achnatherum splendens and Paspalum distichum grew in the plastic film mulching lemon orchards, but didn’t in the open lemon orchard. Total weed density was significantly decreased in the plastic film mulching lemon orchard compared to the open lemon orchard. Digitaria sanguinalis, Ageratum conyzoides, Bidens pilosa and Borreria latifolia were the dominant weed species in RG plot; Cynodon dactylon and Kyllinga brevifolia were the dominant weed species in RH plot; Digitaria sanguinalis and Ageratum conyzoides were the dominant weed species in RI plot.The densities of Kyllinga brevifolia and Cynodon dactylon in plastic film mulching RG and RI plots were significantly lower than those in the open lemon orchard. Bidens pilosa and Borreria latifolia were the indicator species of RG plot; Cynodon dactylon and Kyllinga brevifolia were the indicator species of RH plot; Ageratum conyzoides was the indicator species of RI plot. Thus, plastic film mulching in lemon orchards showed better results on weed control, and the weeds could be maintained at low levels.