The invention discloses an alkaline foam cleanser and a preparation method thereof. The alkaline foam cleanser is prepared from components in percentage by mass volume as follows: 10%-20% of a degreasing agent, 3%-13% of a foam stabilizer, 1%-5% of a bactericide, 3%-9% of a builder, 10%-20% of a cosolvent, 1%-3% of a pH regulator and the balance of deionized water. The foam cleanser has the pH value ranging from 8.5 to 13.5 and is suitable for removal of organic fouling; the degreasing agent and the foam stabilizer can penetrate into biological membranes to dissolve fat, protein and the like; the bactericide kills bacteria hidden in the biological membranes, so that the adhesive force between the biological membranes and objects is weakened, and stubborn stains in fixed places can be quickly stripped and removed. The cleanser is used for cleansing livestock and poultry farms and equipment and has a sterilization effect, so that the following disinfection operation effect is more remarkable. The cleanser is sprayed by a special foam gun after being diluted in the ratio of (1:50)-(1:200).