For filling the room of X ray wood densitometry in China, a wood densitometer, MWMY, was jointly developed by Research Institute of Wood Industry of CAF and Beijing Kexin Institute of Mechanical & Electrical Techniques. This instrument is a combination of mechanics, electronics, optics and computer techniques. In this paper, a brief introduction on the basic functions for MWMY and its flow of the main parts of the software system were presented.