The ship targets in the forward-looking infrared image under sea-sky scene may face problems such as low signal-to-noise ratio and large size difference. In order to better highlight the targets and suppress the background, a forward-looking infrared ship target enhancement method based on multi-scale local contrast is proposed. Firstly, the scene content in the forward-looking infrared images under sea-sky scene is analyzed. Then a new local contrast measure, called Relative Regional Contrast Measure(RRCM) is defined. By changing the size of the grid window, a Multi-scale RRCM(MRRCM) is constructed. Finally, the scale-invariant local contrast image is obtained. The experimental results show that, the proposed method can well adapt to the multi-type and multi-size ship targets in the forward-looking infrared image, which improves the signal-to-noise ratio and signal-to-background ratio of the target signal significantly. Compared with other methods, the ship target enhancement effects of the proposed method is better, especially for small and dim ship target regions. In addition, the proposed method has high operation speed, and can be further accelerated by parallel processing and integral image.