Method for producing caffeic acid by using blue algae

The invention relates to a method for producing caffeic acid by using blue algae, which comprises the following steps of 1) inserting relevant gene segments in plasmid pBluescript II SK+ to obtain recombined blank plasmids; 2) inserting gene segments of nucleotide sequences such as SEQ ID NO.1 among enzyme cutting sites of the EcoRI-PstI incision enzymes of the recombined blank plasmids obtained in the step 1 to obtain recombined plasmids; 3) transforming the recombined plasmids into Synechocystis sp. PCC6803 to obtain transgenic synechocystis; and 4) conducting enlarging cultivation on the transgenic synechocystis obtained in the step 3 and then conducting extraction to obtain the caffeic acid. By constructing homologous recombination carriers for Synechocystis sp. PCC6803 transformation, algal strains capable of producing the caffeic acid under the condition that precursor substance p-coumaric acid is added are obtained through synechocystis transformation, and a new means is provided for the production of the caffeic acid.