The 1.57μm signal light produced by non-critically phase-matched KTP optical parametric oscillator (OPO) pumped by the depleted 1.064 μm Nd: YAG laser after frequency-doubled conversion is injection-seeded into another non-resonant KTP OPO pumped at 532 nm with dual-crystal walk-off compensating configuration. The threshold of non-resonant OPO is reduced by 30% , and energy conversion efficiency is increased by a factor of 5 %.