The characteristic of type Ⅱ noncritical phase matching and the thermal effect caused by high pump power are taken into account. An unidirectional operation is realized by using a λ/4 wave plate, a λ/2 wave plate and a Faraday rotator, and a proper cavity to reduce thermal distortion is designed. An intracavity frequency doubled Nd:YAP/KTP ring laser end pumped by an fiber coupled diode array with output power of 1.0 W at 540 nm is developed. In free running operation, the intensity fluctuation is less than ±1.5%, the frequency stability is better than ±5 MHz.