In this talk, we discuss a reaction-diffusion- advection equation with a free boundary which models the spreading of an invasive species in one-dimensional heterogeneous environments. We assume that the species has a tendency to move upward along the resource gradient in addition to random dispersal, and the spreading mechanism of species is determined by a Stefan-type condition. Under certain conditions we obtain the sharp criteria for spreading and vanishing via system parameters. Also, we establish the asymptotic spreading speed. Some biological explanations are provided. This is a joint work with Harunori Monobe (Tokyo Institute of Technology)