A purely psychological viewpoint would ignore or reject any spritual or supernatural opinions on the meaning of life, and so would focus on the conscious/subconscious, evolutionary, and instinctual goals that humans create.
Most human endeavors come about from a desire to excel or to become personally better. This would be the desire of the Ego to satisfy the Id, which desires enjoyable experiences; the Ego works consciously to create a personal system (standard of living, career) which satisfies those needs. If a person is driven to excel at a sport, it is because the sport is personally satisfying (Ego) and because the admiration of others gives the Id subconscious rewards. If a person just wants to be quietly comfortable, the desire is almost entirely Ego-driven, without Id-driven needs to be seen or respected or even cared-about by others. With this said, the Human Purpose is more than physical satisfactions; the mental and emotional needs of humans can be more important than physical comfort.
In that case, the purpose could be designed around connecting with others and creating a social group that will continue after death. If families are friends for generations, a person can be happy knowing that their memory will continue in the group. Similarly, the drive to have children is a drive to leave something tangible and meaningful of one's self; the child will continue, in its own way, the purposes of the parents.
Bringing these together, the psychological purpose of human life could be defined as a need to live in a manner that is personally satisfying, that allows perpetuation of the Ego after death, and that is either respected by others (Id), or simply allowed without confrontation.
Of course, there are dozens of deeper psychological terms, definitions, and meanings that could be applied to this subject. This is simply one that focuses on the physical, immediate reality of life from a psychological standpoint.