Quantum illumination is a binary hypothesis testing to detect a possible low-reflective object. Theoretically, both cat state illumination and Gaussian-state illumination possess the upper bound of 3dB sensitivity gain, over the usual coherent state illumination, for the significantly low illuminating intensity. Here, we investigate further how to enhance the quantum advantage of quantum illumination by optimizing the illuminating cat states for larger illuminating intensity. By comparing the quantum Fisher information or error exponent, we show that the sensitivity of the quantum illumination with generic cat states proposed here can be optimized further, and the 10.3% sensitive enhancement over the previous cat state illumination can be obtained.