Abstract: In order to limit complexity of the 2-D phased array and its 3-D ultrasound imaging system, a optimal design method of random sparse 2-D arrays based on genetic algorithm is developed. Firstly, the aperture size and the element weights of the array reference is pre-determined according to spatial resolution. Secondly, the sparse ratio is determined according to contrast resolution and the sparse array is designed by randomly removing a fraction of the original set of elements from the 2-D array reference. Consequently, the distribution of the reserved element is optimized by the use of the genetic algorithm to achieve acceptable acoustic properties. The acoustic characteristic of th e sparse arrays is analyzed through continuous wave theory and pulse ultrasound field model based on the spatial impulse response.Results show that sparse arrays based on genetic algorithm have a good overall performance. The main-lobe is practically unaffected by the random removal of elements, and grating lobes are avoided in these arrays, but the average side-lobe level increases a little. However, it can satisfy the needs for the high-quality ultrasound imaging when the sparse array is optimized using the genetic algorithm.