Numerical analysis and experimental results of erbium-ytterbium co-doped double-cladding fiber lasers (EY-DCFLs) with single mode output were presented. Numerical analysis of this EY-DCFL, based on the rate and propagation equations,was performed firstly in order to optimize its properties theoretically. Then experimental research was done of this EY-DCFL by using the same conditions such as pump power, fiber length, and dichroic mirror. The output powers as functions of the input pump power and fiber length were described, as well as the output wavelength vs the fiber length. The maximum output power was about 2.2 W lasing at 1566 nm by using a 6.30 m fiber, with an overall optical to optical conversion efficiency of 22%, which were 33% lower than the calculated