Cloud computing technology not only provides us powerful computing, on-demand service, rapid elasticity, but also possible great destruction by the internet criminal accordingly. This prompts us to consider the cloud-based worm propagation problem. We set up the analytical model through a highly abstract network environment and achieve the overall characteristics of the worm research purposes. In this paper, we firstly analyze the factors affect worm scan and propagation in the cloud and put forward a novel cloud-based worm model: the MapReduce Divide-and-Conquer model (MRDC). Secondly, we analyze the architecture and performance of MRDC worm contrast to Code Red, the hit-list worm, and flash worm, etc. the simulation shows that the MRDC worm significantly improves the worm propagation. And finally, we discuss some threat trends of cloud-based worm propagation and some possible solutions. Our simulation shows that the MRDC worm propagate much faster than the other worms that the MRDC worm can scan and infect entire IPv4 space in no more than 10 minutes, the perfect MRDC worm can infect 360,000 vulnerable machines in no more than 1 second and all vulnerable machines in the entire IPv4 space in no more than 10 seconds.