A new Yb-doped silicate Yb³⁺∶Sc₂SiO₅ (Yb∶SSO) has gained considerable attention in recent years because of its advantageous laser properties. Thermal lens focal length of Yb∶SSO in the case of different pump powers is calculated theoretically, and the influence of the material negative refractive index on the laser is analyzed. Quasi-continuous wave (QCW) lasing performance of the Yb∶SSO end-pumped by a 976 nm laser diode (LD) in a plane-plane cavity is studied. Laser output with peak power of 27.6 W and optical-to-optical conversion efficiency of 21.4% is obtained when pump laser is with repetition rate of 50 Hz, pulse width of 500 μs and peak pump power of 128.8 W. Meanwhile, beam qualities (M² factors) in x and y directions are 1.24 and 1.20, respectively. Finally, the law of center-wavelength movement caused by the change of pump power is observed, and the cause of dual-wavelength asynchronous oscillation is theoretically analyzed.