The invention discloses intramuscular injection solution for enhancing immunity. Pidotimod and sodium hydroxide or potassium hydroxide or arginine and the like are reacted in water or ethanol or mixed solution of water and ethanol so as to generate pidotimod sodium salt, potassium salt or arginine salt, and then the injection solution is prepared. The intramuscular injection solution is characterized in that: the pidotimod which is an active component in the injection solution exists in the form of the pidotimod sodium salt or the potassium salt or the arginine salt, and the pH value of the solution is within 4.0 to 6.0. The optimal range of the pidotimod or the pidotimod sodium salt or the potassium salt or the arginine salt in every 1ml injection is within 50 to 250mg. The preferential specification is 2ml: 0.2g or 3ml: 0.2g (according to the pidotimod). The injection solution is used for treating the following diseases: (1) repeated upper and lower respiratory tract infection (pharyngitis, trachitis, bronchitis and amygdalitis); (2) repeated infection of otorhinolaryngology (rhinitis, nasosinusitis and otitis); (3) infection of a urinary system; (4) infection of gynaecology; (5) clinical patients with poor cellular immune function after chemotherapy; (6) specific and non-specific immunodeficiency diseases such as cancer and the like. The injection solution is used for reducing the acute disease attacking number of times, shortening course of the disease and relieving the attacking degree. Moreover, the injection solution can also be used for adjuvant therapy of antibiotics when in acute infection.