Nanorobots are a kind of robots that can operate in extremely small space and will be widely used in the future. Once the nanorobots are applied, the space as large as the size of a traditional robot can accommodate trillions of nanorobots. Only by means of the cloud computing technology can such immense numbers of robots can be effectively controlled, since the cloud computing is able to manage and control considerable numbers of resources. Yet, at present, there is no research into the cloud nanorobots, so this paper first proposes and studies the cloud nanorobots. Although there are studies on cloud robotics, the existing researches on cloud robot mainly focus on how to use cloud computing to share data among robots, provide robotic applications as cloud services, and increase the robot processing ability of applications. However, no researches focus on how to make use of cloud computing to promote the extendibility, scalability and fault-tolerance of multi-robot system. Since in the applications of other types of robots, it is hugely difficult for over a thousand of robots to work together, and the requirements of the extendibility, scalability and fault-tolerance for the cloud robots is not demanding, no sufficient attention is paid to the extendibility, scalability and fault-tolerance of cloud robots. With the accelerated popularization of robots in factories and tons of households, nevertheless, the problem of the extendibility, scalability and fault-tolerance of large system with many robots is increasingly serious. This problem will be more severe in the multi-nanorobot system, since trillions of nanorobots always need to work in the same application, thereby contributing to exceedingly serious problems of extendibility, scalability and fault-tolerance. If these problems are not resolved, the cloud nanorobots are easily broken down, make mistakes and thus cannot function properly. What's more, the cloud nanorobots tend to be applied in very important fields such as medical care and production, and major significant economic loss and even loss of life will be caused by the breakdown or errors of the system. Therefore, multi-nanorobots are in a burning need of the extendibility, scalability and fault-tolerance of the cloud system. The extendibility, scalability and fault-tolerance problems can be summarized as: 1. How to unlimitedly extend the number of robots? 2. How to add or remove robots in a real-time, large-scale manner and deal with the sharp changes of task load? 3. How to make the robot collapse and failure not affect the system? This paper studies the problems and proposes the extendibility, scalability and fault-tolerance methods for cloud robot especially for cloud nanorobots. Copyright © 2015 American Scientific Publishers All rights reserved.