Generally,a magnetic target can be described with six parameters,three describing the position and three describing the magnetic moment.Due to a lack of sufficient components from one magnetometer,we need more than one magnetometer when locating the magnetic target.Thus,a magnetometer array should be designed.The baseline of the array is an important factor that affects the localization accuracy of the target.In this paper,we focus on the localization of a static target by using a scalar magnetometer array.We present the scalar magnetometer array with a cross-shaped structure.We propose a method of determining the optimal baseline according to the parameters of the magnetometer and detection requirements.In the method,we use the traditional signal-to-noise ratio (SNR) as a performance index,and obtain the optimal baseline of the array by using the Monte Carlo method.The proposed method of determining the optimal baseline is verified in simulation.The arrays with different baselines are used to locate a static magnetic target.The results show that the location performance is better when using the array with the optimal baseline determined by the proposed method.