When should I do stretching exercise to gain height? Before running or after running?

Doesn't raise height. Most people reach their maximum height in their late teens. Without nutritional problems or chronic childhood illnesses, height is largely based on genetics and parental heights. Aside from eating right, exercising, sleeping well, and being happy, there's not much a person nor his doctor can do to increase height. In rare cases, growth hormone is approved for use in young, extremely short kids.