Diode pumped alkali vapor laser (DPAL) has applications in many areas and is developed rapidly in recent years. A diode laser array with center wavelength of 780 nm is used as the pump source for the Rb laser, and a Littrow external cavity is built with a plane diffraction grating to narrow the linewidth of the diode laser to 0.13 nm. A chopper is used to change the continuous diode laser to pulsed laser. The diode laser is beam shaped, a lens group is used to twist the beam to nearly square shape. After linewidth narrowing and beam shaping, the diode laser is focused on a Rb vapor cell which is filled with Methane as buffer gas at the pressure of 79 kPa. With the maximum peak power of 13 W injected into the Rb laser resonator and the temperature of the cell kept at about 145 ℃, the linearly polarized Rb laser with peak power of 2.8 W is obtained, and the optical to optical efficiency is 21%.