We have demonstrated a high-power intracavity-pumped doubly resonant optical parametric oscillator (OPO) at 2 lm with single-type II phase-matched KTP. A linearly polarized Q-switched solid-state Nd:YAG laser was used as the intra-cavity pump source, of which the output power and beam quality were improved by cascading two laser rods for compensating the thermal birefringence as well as by placing double acoustic-optical Q-switches orthogonally, and the output power of the doubly resonant OPO was studied versus the temperature of KTP and the repetition rate of the Q-switch. The output power was insensitive to the temperature of KTP in a wide range, and 70-W average power was obtained at 2 lm with the repetition rate of 5 kHz. The stability of the OPO laser was measured to be \3.5 % root mean square at the output power of 70 W for 400 s.