Highly efficient passively Q-switched Yb:YAG ceramic laser with Cr4+:YAG crystal as saturable absorber is achieved. Maximum average output power of 0.96 W is obtained when the absorbed pump power of 3.8 W is used; corresponding optical-to-optical efficiency is about 25%. The slope efficiency is 30%. Laser pulses at 1 030 nm with pulse energy of 107 μJ and pulse width of 9 ns are achieved at repetition rate of 9 kHz, with corresponding peak power of 11.9 kW. Meanwhile the effects of absorbed pump power on the characteristics of passively Q-switched laser pulses are investigated systematically.