A game server includes: a main processing unit, connected to a user terminal via a data network, configured to perform user login; and a game processing unit configured to control the user terminal to execute a puzzle game in response to a game execution request signal from the user terminal. The game processing unit is configured to: control the user terminal to display colored blocks arranged in a matrix form of N rows and M columns in a puzzle game area, and to display one game character in an action display area; exchange a selected block with another neighboring block based on user input; determine if a matching block group of at least three consecutive blocks having the same color results from the block exchanging step; remove the matching block group; and control the game character to perform an action according to a result of the block removing step.