Effect of thermal lensing is the main obstacle of getting high power and good beam quality in laser diode (LD)-pumped solid-state lasers. A theoretical investigation of effects of thermal lensing in an end-pumped Nd∶YVO4 laser is demonstrated using finite-element-method, showing that the thermal lensing effect in high power LD-pumped Nd∶YVO4 lasers is very serious, particularly the end deformation which accounts for 50% of the overall thermal lensing effect. The employment of a composite crystal has been demonstrated to be a useful method in relieving the thermal lensing, resulting in higher output power and better beam quality. The fundamental mode output power as high as 11 W has been achieved with 23 W pump power in composite crystal, the beam quality factor M2 is less than 1.5, and O-O conversion efficiency is up to 48%.