An ultrashort cavity single-frequency Distributed Bragg Reflector (DBR) laser operating at 1064 nm was proposed with a cavity length of 2 cm, and the gain medium is a 1.1 cm long highly Yb-doped silica fiber. With a proper temperature control, the stable single-frequency laser with a linewidth of 4.8 kHz was achieved. The maximum output power of the DBR fiber laser is 13 mW with a slope efficiency of 3.4% relative to the launched pump power of 378 mW. The measured relative intensity noise is about －132 dB/Hz at frequencies of over 1 MHz. The master oscillator power-amplifier structure was used to amplify the output power of the DBR laser. When the length of the amplification gain laser is given as 56 cm, the output power is scaled up to 325 mW with a slope efficiency of 52.8%.