3d model construction through webcam

I want to move a 3d object according to the motion and speed of real object through webcam.
is there any library available for this work ?

There are various libraries depending on your need. Augmented reality (AR) frameworks does it, Vuforia is one of the famous ones in this. But there are a lot of frameworks available depending on the need, just google for AR in Unity3d.

Another method is using openCV to process the webcam data and find the object present in it and you can find whole lot of information about it in this link and its forums. EmguCV is the port of OpenCV in c# that can be integrated into unity projects(if it is PC based). Note that the AR plugins does the same, so it is wise to go for it unless you need to experiment things or have a different need.