A method for detecting driving behavior and a system using the same is disclosed. Firstly, at least one user image comprising an arm image and a head behavior image is retrieved. Then, a processor retrieves the arm image to compare with arm sample images stored in a database. The arm image corresponds to the arm sample image to determine a normal driving behavior. The arm image does not correspond to the arm sample image to determine an abnormal driving behavior, whereby the processor retrieves the head behavior image to compare with head regulation-violating sample images stored in the database. The head behavior image does not correspond to the head regulation-violating sample image to determine a normal driving behavior. The head behavior image corresponds to the head regulation-violating sample image to determine an abnormal driving behavior and output a second-level warning signal, thereby warning a driver.