Sidetracking in open hole is one of the most popular drilling technologies. Unknowing sidetracking or only with single sidetracking method, the construction time would be longer, more well sections would be lost with tools and instrument loss, even with failure. Some key problems of sidetracking are studied and discussed in this paper; principles of kick-off point are given and the evaluation of tools and control drilling by time or weight on bit are brought forward. In addition, sidetracking in a well is taken as an example to describe the technologies.