The invention relates to the field of distance measuring devices, in particular to an intelligent tree diameter measuring laser gun and a tree diameter measuring method. A laser distance measurement principle is used, distances from laser points to a tree are measured by three lasers on the laser gun respectively, a tree diameter can be calculated by utilizing a function formula due to fixed angles among the three lasers, a measured result is uploaded to a mobile terminal automatically through a wireless network, after a worker determines the measured result on the mobile terminal, the determined result is uploaded to a Cloud for back-up, and mobile terminal data and Cloud data are automatically and synchronously updated. The intelligent tree diameter measuring laser gun and the tree diameter measuring method disclosed by the invention have the beneficial effects that the device is reasonable in structure, convenient to use, high in reliability and high in measurement accuracy; the operation is simple, easy and convenient, one worker is enough to perform the operation of tree diameter measurement, and automatic measurement, real-time display by a liquid crystal screen and automatic record can be performed by just pressing a measurement press key; the equipment is low in cost and can be widely popularized; the device can also be applied to measurement work in other fields; and during tree diameter measurement, the data is stored in the Cloud at the same time, so that the data is backed up and is also convenient for a person at a far end to look over.