A micro-cavity measuring equipment based on double optical fiber coupling includes a sight and transmitter, a controller, and a length measuring device. The equipment detects small changes in the position of an object with respect to a probe from a moment when the sight and transmitter starts working to another moment when the sight and transmitter stops working. The controller has a program to automatically control the whole measuring process. The measuring equipment is characterized in that the sight and transmitter consists of a laser unit, a data collecting and processing unit, and a double optical fiber coupling unit with its ends of incident and effluent optical fibers fixed on a coupler. A micro-cavity measuring method based on double optical fiber coupling consists of the following steps: inserting the probe into the micro-cavity and moving it in the measuring direction; sending signals to the length measuring device by the sight and transmitter to cause the length measuring device to record the corresponding position of the probe when the probe is contact with the sides of the micro-cavity; and then calculating the dimensions of the micro-cavity.