Based on self-imaging confocal resonator,in-phase locking of two Yb-doped fiber lasers has been realized using a flexible experimental setup.With near-field filling factor being 10.86%,15.2%,25.33%,the number of side lobes of interference fringes decreases and the energy ratios of central lobe are 13.58%,18.98%,31.42%,respectively.When pump power is 8.8 W,a coherent combining laser output of 1.44 W is obtained,with a power combination efficiency about 93.4%.Analytical results suggest an optimal fiber length and a smaller reflectivity of output coupler contribute to higher laser slope efficiency,which increases coherent combining output power.