Acoustic vector sensor consists of pressure and panicle velocity sensors, which measure the three-dimensional acoustic particle velocity, as well as the pressure at one location at the same time. By preserving the amplitude and phase information of the pressure and particle velocity, they possess a number of advantages over traditional scalar sensors. Signal-to-noise ratio (SNR) gain (which is often called array gain) is one of such advantages and is always interested by all of us. But it is not unchangeable if the spatial correlation of the noise field varies. Much more important, it is difficult to be given if the noise becomes complex. In this paper, spatial correlation of the vector field of isotropic volume-noise and surface-generated noise has been introduced briefly. Based on the results, the combined SNR output of a vector linear array is investigated and the maximum gain is given in the specified noise. Computer simulation shows that the output of one array in the same noise is not the same in different gestures. And then we find the best gesture through SNR calculation and obtain the biggest gain, which has important meaning to guide how to deploy an array in practice. We also should use the array with respect to the characteristics of the real ambient noise, especially in anisotropic noise field.