High efficient pulse output from a large size rectangular core crystalline waveguide actively Q-switched laser was achieved experimentally. A crystalline waveguide, with a rectangular core size of 320μm×400μm by 1.0at.% Yb:YAG (core), 600μm×600μm by 0.5at.% Er:YAG (cladding), and 7mm×7mm by 4.0at.% V:YAG (outside of the cladding) was designed and fabricated. Using a continuous diode laser as an end pump, an output pulse energy 1.75mJ@10kHz, pulse width 9.9ns (peak power 175kW), optical-optical efficiency 26%, with the beam quality of Mx2=1.15, My2=1.10, were obtained in the experiment. The design method that used to suppress amplified spontaneous emission (ASE) and parasitic oscillation by cutting off the reflection and transmission paths, can be applied for various kinds of crystalline waveguide Q-switched or mode-locked lasers.