The scope of this paper addressed the problem of detecting a dim moving target from a sequence of multispectral IR cubes. The detection problem was formulated in a general framework, assuming unknown target amplitude, position and velocity. This composite hypothesis testing problem was approached by means of the generalized likelihood ratio test (GLRT) theory. The detector structure and its actual implementation based on velocity filters were discussed in detail. Approximated expressions of the false alarm and detection probabilities were obtained and validated by means of simulation. To test the effectiveness of the detection algorithm, the detection results obtained on a set of synthetic multispectral IR image sequences were presented and discussed. These results indicate that the algorithm proposed can obtain a good performance on dim target detection with low SNR.