For dogs, jumping is a normal behavior that they display without knowing that there are times when it is not acceptable. To your Shih Tzu, jumping on someone is just a method to communicate a friendly hello.
will usually jump up on people more than older dogs; however canines of any age may display this friendly behavior.
The other type of jumping that a Shih Tzu will do is the type that is shown during play.
If an owner "play wrestles" with their dog, most likely the dog will become very excited and will jump up.
The aspect that is important is that if a dog is allowed to jump up to say hello to people and allowed to jump during play, they may inadvertently jump on a young child, knocking them down at best and causing harm at worst; not to mention that having a dog jump on a child usually is scary for that youngster.
If you have young children in your home, you will want to train your Shih Tzu (or other dog) to refrain from jumping so that your child does not become afraid of the dog or that there are any accidents.
As the child grows older, he or she may end up wrestling with the dog and not minding the jumping at all.
Most owners will also want to maintain some type of control over this behavior in the case of visitors who arrive at the home and do not want a dog jumping on them.
All dogs can be trained to stop jumping on people, just as any other type of actions that one wishes to control.
The key to training your dog is to emphasize good behavior with tons of praise, kind words, treats, pats, kisses and hugs.
Whenever your Shih Tzu behaves in the way you wish for them to, make sure that they know it.
When your dog behaves in a way that you do not approve of, make sure that they know that also!
Of course, never hit or yell at your dog; but you should say "No" in a stern voice and physically bring the dog down from the jumping position.
The #1 rule of training for any type of unwanted behavior is to 100% completely and utterly ignore the behavior and give reward & attention for wanted behavior. When behavior is as physical as this, placing your Shih Tzu in his playpen or other designated area for a short 'time out' will often work well.
It takes a dog about 15 minutes to realize that he is being ignored and for that sort of temporary 'banishment' from the 'pack' to have an effect. More often than not, once that realization has settled in, a dog will behave once he is released from his timeout and is brought back into the fray of the family.