Lower limb inequality, commonly known as “long and short legs,” is a relatively common condition in children, and treatment varies depending on the cause and prognosis. To get the right treatment, we must first identify the cause of limb inequality. Limb inequality can be broadly divided into two categories, true inequality and pseudo inequality. We explain them separately below. True limb unequal length, that is, bilateral lower limb bony length is not really equal, in general, our normal people’s two sides of the lower limbs are not exactly equal, but generally the difference is not more than 1cm, in adults even if the difference of 2cm is also acceptable. In children, due to the age difference, the value of the difference that will cause clinical symptoms is not yet determined, and in general more than 1.5 cm will be limping gait. The main causes of true inequality are the following: 1. stagnation or slowing of limb growth caused by epiphyseal plate injury, such as osteomyelitis involving the epiphyseal plate, premature closure of the epiphyseal plate caused by epiphyseal plate injury, various tumors and tumor-like lesions involving the epiphyseal plate (multiple osteochondromas, Ollier’s disease, bone cysts, etc.); 2. bone defects, such as bone necrosis, resorption, and bone discontinuity caused by various injuries or inflammatory diseases; 3. 3. unilateral limb hypertrophy; 4. epiphyseal necrosis and collapse due to ischemic necrosis of the femoral head. For true limb inequality, in addition to the treatment of the cause, Ilizarov technique can be used to lengthen the limbs to equal length of both lower limbs. Pseudo-limb inequality mainly includes several cases: one is joint dislocation, mainly hip dislocation, such as developmental hip dislocation in children. The second is pelvic tilt, there are many causes of pelvic tilt, often not easy to identify the exact cause and treatment can not start, common causes of pelvic tilt are scoliosis, pelvic fracture, hip tumor, hip trauma hip muscle fascial contracture, especially unilateral hip muscle contracture, because the period symptoms and signs are completely different from bilateral hip muscle contracture, often difficult to confirm the diagnosis. Thirdly, joint effusion, a large amount of hip effusion can also occur in the case of bilateral limb inequality. In conclusion, the treatment of limb inequality is a complex process that requires doctors to have sufficient knowledge and experience to identify the causes in order to obtain good treatment results.