A laser diode dual-end-pumped, single-frequency Q-switched Nd:YAG laser is implemented. Single-frequency seed injection is realized by utilizing an RbTiOPO4 (RTP) crystal as the intracavity phase modulator to modulate the length of the cavity, which leads to the single longitudinal mode output. Adopting another pair of RTP crystals as a Q-switcher, the laser is capable of generating 7.5 mJ pulse-energy with 14.6 ns pulse duration, and 45 MHz linewidth at 900 Hz repetition rate. The beam qualities M2 of 1.30 in the horizontal direction and 1.36 in the vertical direction are obtained. The frequency stability is 1.1 MHz and the linewidth stability is 0.52 MHz over 2 min laser output. In conductively cooled structure, the output of single-frequency pulsed laser with narrow linewidth, high frequency stability and high linewidth stability is obtained.