A method for diagnosing leakage of a fuel vapor dual purge system is provided. The method includes determining whether an operation region of a vehicle is an operation region in which a turbocharger is operated and adjusting a flow amount of intake air flowing into the turbocharger according to an operation region in which the turbocharger is operated. A hydrocarbon collecting amount of a canister connecting fuel vapor generated in the fuel tank is calculated and a flow amount of the fuel vapor passing first and second purge lines is adjusted. A leak of the fuel vapor is diagnosed in the first purge line and the second purge line.