1. A mobile application search system, comprising: a user interface unit that provides an input environment to allow a user to input a user query and displays a mobile application search result related to the user query; and a mobile application search engine that receives the user query from the user interface unit and searches for a mobile application related to the user query using an activity knowledge database in which a list of elements involved in achieving a plurality of goals that people desire in daily life is stored, wherein the mobile application search engine is configured to: receive the user query of a text form; convert the user query of the text form into a query language query; calculate semantic relevance between two concepts using the activity knowledge database so as to calculate a search score between text data of the mobile application and the query language query; calculate a translation probability between the conceits based on the semantic relevance between the concepts; calculate a semantic-based search score between words included in text data of the mobile application on a knowledge-based search model generated using the translation probability between the concepts; calculate a semantic-based search score of the mobile application using the semantic-based search score between the words; calculate a final search score of the mobile application by combining the calculated semantic-based search score of the mobile application with a keyword-based search score; and output a high rank search result which is a search result of the mobile application corresponding to a high rank according to a predetermined criterion among the search scores of the mobile application.