A finite-difference seismic modeling method based on triangular grids is presented. Compared with the conventional finite-difference schemes based on rectangular grids, curved velocity boundaries can be more accurately represented by using the new approach. Models with an irregular earth surface can be directly used for seismic modeling without special processing. As the space steps can be varied with velocities and the explicit finite-difference scheme is used for calculation, the method is an effective improvement over the conventional finite-difference methods. Numerical tests demonstrate that this new method is stable, efficient and sufficiently accurate.