A low-profile differential-fed microstrip patch antenna (MPA) with high-gain and wide-beamwidth under dual-band by multi-resonant modes is proposed in this paper. Firstly, the dielectric constant of the substrate is properly selected to achieve wide HPBW at TM10 mode. Then, the gain is improved via a linear slot on the patch on upper band at TM30 mode and two ring slots are etched around the coaxial inner to achieve impedance matching in dual bands. Finally, the simulated results reveal that the HPBW of the proposed MPA is increased to around 134 deg at lower band and the gain of 9.63 dBi is acquired at upper band simultaneously. Meanwhile, it keeps a low profile of around 0.0270.