A high effect green laser is realized by acousto-optic (A-O) Q- switched intracavity frequency doubling Nd∶YVO4 /KTP laser,which is formed with a simple two-mirror line cavity.The TEM00 mode green light power of 999 mW is obtained with 1 608 mW of an input 1 064 nm fundamental pump power at the pulse repetition rate of 40 kHz.The corresponding to optical-optical conversion efficiency is up to 62.1%.The spectral width (full width at half maximum) of green laser is about 0.11 nm or less.±1.2% instabilityof output power is obtained.