The output characteristics of a passively Q-switched pulse laser with a large core size crystal waveguide are studied experimentally. Using Yb∶YAG with core size of 320 μm×400 μm and an atomic number fraction of 1%, Er∶YAG with cladding size of 7 mm×30 mm and an atomic number fraction of 0.5%, a single-clad rectangular crystal waveguide with a length of 77 mm, and a Cr ⁴⁺∶YAG saturable absorption crystal with initial transmittance of 85%, a passively Q-switched pulse energy of 0.84 mJ@8.7 kHz, a pulse width of 23.8 ns, and a beam quality of M²=1.12×1.06 is obtained. Experimental results show that the high peak power pulse output with near diffraction-limit can be obtained by passively Q-switched pulse laser with large core diameter crystal waveguide.