In this paper, a method of time-resolved divergence measurement using an aperture is reported. With this method, we measured the evolution of the beam divergence of output pulse from an injection locking copper vaper laser (CVL) of magnification M=10 (M=30 for oscillator). The experimental results show that the beam divergence becomes smaller and smaller reducing from 1.0 mrad to 0.12 mrad. The experimental results are analysed.