A second harmonic generation system with two type II KDP crystals in quadrature is optimized for the nanosecond chirp pulse. The acceptance bandwidth of this optimizing scheme is close to 10 nm by using two crystals with slightly opposite angular detuning from phase matching and the conversion efficiency can reach 70% for top-hat chirp pulse at ～2 GW/cm2 in theory. The preliminary experimental results are obtained on the 9th beam of Shen Guang II SGII laser system, and the performance of optimization is partially verified.