1. A method for detecting a cross-platform difference of a web application comprising: generating a first relative layout model based on a first relationship between a plurality of elements of a screen of a web application when the web application is executed on a first platform; generating a second relative layout model based on a second relationship between the plurality of elements of the screen of the web application when the web application is executed on a second platform; and determining a difference between the first relationship and the second relationship based on a comparison of the first relative layout model with respect to the second relative layout model.