The fabrication of a twin-core erbium-doped fiber (TC-EDF) is reported. The twin-core erbium-doped fiber with single core doped is fabricated by modified chemical vapor deposition (MCVD) and photonic crystal technology. The characteristics of the twin-core erbium-doped fiber are numerically simulated by using coupled mode theory and rate equations. Meanwhile, a twin-core erbium-doped amplifier is established and measured experimentally. It is presented that this type of twin-core erbium-doped fiber is well fit for gain equalization.