Abstract: Vector hydrophone measures pressure and all three orthogonal components of particle velocity at a single point in space. Using those obtained amplitude and phase information is very useful for improving detection and estimation of sonar. The spatial correlation between pressure and particle velocity in 3-D spherical isotropic noise field is investigated. Noise covariance matrix is derived; one of horizontal and vertical array is shown, respectively. Noise covariance matrix of a single vector hydrophone is studied with experiment results in the shallow water. Array gain of acoustic energy flux is also derived using above theoretical results.