In this article, a novel ac electro-magnetic trap for neutral atoms is proposed, which is based on the interaction of a magnetic dipole moment of trapped atoms with both an ac quadruple magnetic field in the transverse direction and a dc-bias magnetic field along the axial direction. The result shows that this is an ideal strong field-seeking trap for cold atoms. An atom guide with radial trapping potential over 1.2 mK is obtained and the guided atoms can be confined in a small region of r～50 μm. With changing the distribution of the bias magnetic field, an ac magneitc trap of cold atoms with axial potential depth 0.5 mK and radial potential 0.6 mK can be got, which is high enough to trap nearly all atoms with a temperature of ～120 μK.