The invention provides an industrial method for extracting natural L-
citrulline from
plant tissues of watermelons or
citrullus lamatus, and the like, which belongs to the technical field of extracting natural products in the
food industry and the
medicine industry. The watermelons, the
citrullus lamtus or the stems and leaves thereof are taken as raw materials, and the extracting process comprises the following steps: firstly, the raw materials are washed clean and broken to separate the watermelon peel from the watermelon pulp for respectively extracting juice; the two juices are mixed, and micro-
filtration and ultra-
filtration are carried out to remove insoluble substances and
macromolecular substances; and then
reverse osmosis and nano-
filtration are carried out to obtain the filtrate; the pH value of the filtrate is regulated and then a macroporous strong acid cation exchange resin column is added; and then
ammonia water is taken as an eluant for
isocratic elution; the eluent obtained is decompressed, distilled, deaminized, discolored, condensed and crystallized to obtain a white crystalline product of the natural L-
citrulline extracted from the watermelons. The prepared product is a pure
natural product without harmful substances and has high purity and good quality, thus the natural L-
citrulline can be directly taken as a
food additive and
raw material of health products or medicines.