1. A method for image decoding which supports multiple layers, the method, comprising: analyzing a video parameter set (VPS) extension for layer dependency on a current layer; analyzing slices for layer dependency on a current slice by determining whether not to apply layer dependency to the current slice or to apply new layer dependency to the current slice, the new layer dependency determining within a range of layer dependency analyzed from the VPS extension; and constructing a reference picture list about the current layer based on at least one of layer dependency analyzed from the VPS extension and layer dependency analyzed from the slice, wherein the layer dependency is composed of at least one reference layer set including the number of reference layers which the current layer references and identifying information of the reference layer.