Frequency stabilization of a diode laser at 480 nm is crucial for coherently exciting rubidium atoms to Rydberg states. A laser frequency stabilization technique is reported based on electromagnetically induced transparency in a ladder configuration with a polarization spectrum stabilized 780 nm diode laser as the probe laser and a 480 nm laser as the coupling laser. With a uniform magnetic field, a two-photon dichroic atomic vapor laser lock (DAVLL) spectroscopy was generated. Then this spectroscopy was fed back through two proportion-integral-differential circuits to lock the 480 nm diode laser. A combined linewidth of about 1 MHz is achieved during the locking period.