The invention relates to the field of daily chemical products, in particular to a plant source antibacterial agent and a preparation method thereof. The plant source antibacterial agent comprises thefollowing components in parts by weight: 20-33 parts of a pulsatilla cernua extract, 14-36 parts of a Chinese prickly ash extract and 20-38 parts of a tillandsia usneoides extract. The plant source antibacterial agent provided by the invention has a very high property of inhibiting growth of bacillus subtilis, escherichia coli, staphylococcus aureus, candida albicans, pseudomonas aeruginosa, aspergillus niger and the like, and a preservative property as well, besides, the stability of the agent can be also very well improved at a high temperature. In addition, cosmetics can be kept gentle whenantibacterial effects and high-temperature stability are maintained, and the agent has the characteristics of being non-toxic and non-irritant to human bodies.