Focusing on the prediction accuracy of interval grey numbers, grey prediction models based on function transformation of cotangent are established by investigating four typical trends of interval grey numbers sequences respectively. According to different trends of interval grey numbers sequences, the approaches can be applied to the upper bound and lower bound sequences of interval grey numbers or the kernel and measurement sequences of interval grey numbers variously. By this means, this paper effectively extends function transformation technology to the field of interval grey numbers for grey prediction. Finally, numerical examples and a case are given to illustrate the effectiveness and practicability of the improved model.