In order to obtain the magnetic gradient tensor of magnetic target, the method of rotating-calculating magnetic gradient tensor was proposed. The enough magnetic gradient data can be measured by rotating the magnetic gradiometer about the vertical axis, and it is used to calculate the magnetic gradient tensor. The difference of the magnetic gradient tensor between theoretical value and measurement value was used as the reference, and the rotation angle, inclination angle and baseline length of calculation model were optimized. The influence of three-axis pointing error of magnetometer on the calculation result of magnetic tensor was analyzed. The simulation results show that the proposed method is effective in calculating the magnetic gradient tensor. There is little difference between the calculated value and the theoretical value.