The invention provides a device and a method for manually measuring normal thickness of a large cavity deep radome. The device comprises a radome measurement fixing device and a handheld radome normal thickness snap gauge, wherein the radome measurement fixing device comprises a measurement table, a radome shelf, a large-end fixing clip and a small-end fixing clip; and the handheld radome normal thickness snap gauge comprises a measurement main support, a reinforcing frame, a measurement micrometer head, a measurement micrometer head support, an inner measuring rod, an inner measuring rod support, a positioning micrometer head, a lengthened positioning rod and a positioning micrometer head support. The device has a composite measuring rack structure; the structure of the measurement snap gauge is designed optimally; and the measurement snap gauge can be light under the condition that the structural strength is guaranteed. The positioning measurement method is implemented by using the micrometer head, and a measured angle can be accurately and quickly positioned. The device has the advantages of high precision, low cost, convenience in operation and the like. Moreover, the device and the method have remarkable application value on measurement of the normal thickness of the radome.