rigibody's jumpping

I am coding the jump function on my 3d game,
while I cannot make it as I expected.
I expected my character can jump as how Mario jump,
(neglected the small or big jump)

While my character jump with a very quick speed,
and even it will fall on to the ground.

I have set the Edit->project setting->physics's gravity to y=-500
with the character rigibody's mass=5,
drag=0 and
angular drag=0.05

A video describe my problem
https://www.youtube.com/watch?v=-NKpMFsjNMk&feature=youtu.be

With my code

 void FixedUpdate () {
         myPlayer.updateCharacterMovement ();
         checkJump ();
 
     }
     
     void checkJump(){
         if(Input.GetKey(KeyCode.Space)&&isGrounded){
             jumpCharacter();
         }
     }
 
     void jumpCharacter(){
         myPlayer.rb.AddForce (new Vector3(0, 500, 0), ForceMode.Impulse);
         isGrounded = false;
     }
 
     void OnCollisionEnter(Collision collision){
         Debug.Log (collision.gameObject.name);
         if(collision.gameObject.layer==LayerMask.NameToLayer("Terrain")){
             Debug.Log ("Ground");
             isGrounded=true;
         }
     }