The invention discloses a preparation method of an antireflection film on the outer surfaces of an infrared optical window and an optical lens, and relates to the technical field of optical film preparation. After an antireflection film substrate is cleaned, a power supply of a coating machine is turned on, a mechanical pump is started, and a pre-valve is opened to extract waste gas in the coating machine; high vacuum pumping is conducted on the anti-reflection film base body, when the frequency reaches 100 Hz, the low valve is closed, the pre-valve and the high valve are sequentially opened, and the vacuum is recovered to reach 6.0-6.5 E <-3 > Pa; heating the antireflection film substrate in a vacuum chamber, performing airflow control on the vacuum chamber, respectively putting zirconium oxide, silicon dioxide and titanium dioxide for coating into three crucibles of a coating machine, starting evaporation coating, and preserving heat after coating is completed; and finally, the coating machine and the equipment power supply are turned off, and the part is taken out after waiting for 12-16 hours. According to the invention, the requirement of cold reflection of an optical system is finally met, and the optical window can be wiped by absorbent cotton after being subjected to environmental corrosion of a salt spray test and a mould test for a long time, so that the optical window and the appearance meet the requirements.