Airborne linear array 3D SAR imaging technique is a research focus in the field of radar imaging, and has broad applications in military and civilian. It utilizes a linear antenna array on the wings to obtain an expected resolution in cross track direction. And imaging performance would be influenced by the array configuration directly. As the wings can not be long enough to carry many T/R elements, it is valid to acquire good imaging performance via MIMO radar array. In this paper, array design issue of airborne linear array 3D SAR system is investigated. Based on the spatial convolution principle, the operation law of inversed convolution is summed up. Multiple design methods of linear MIMO array for 3D SAR imaging system are proposed through inversed convolution operation. Then the advantages and disadvantages of each design method are analyzed in the view of imaging properties. The investigation can provide technical support to construction of airborne linear array 3D SAR imaging system.