The present invention relates to a natural language based service selection system for complementing incomplete queries, which comprises a semantic analyzing device which analyzes an incomplete query from a user semantically, a service selecting device which complements the incomplete query based on the semantic-analyzed query so as to acquire the corresponding selected service, and a retrieving device which retrieves an answer according to the selected service. The present invention also relates to a natural language based service selection to method as well as a service query system and method thereof, and thus can process an incomplete query from a user and provide a selected service.