The invention relates to a testing device and method for a compression deformation modulus and strength of a soil body in a deep hole. Load plate test is the most direct and reliable way for evaluating engineering foundation state; however, no device is available for an in-hole load plate test at present. According to the testing device, a supporting ring is coated with a hydraulic rubber film; the supporting ring is assembled on a supporting plate outside a bottom center pipe; then a jack and a pressure sensor are connected with the top of the bottom center pipe and a displacement sensor is fixed on the supporting ring; a top center pipe is coated with an air pressure rubber film and upper and lower cover plates are fixed; a testing system is arranged; and an air pressure pump and a hydraulic pump are started to record measured values of the pressure sensor and the displacement sensor. According to the testing device and method, an independent in-hole load plate testing system is composed of an air pressure friction reaction-force device, a loading device and the testing device; a supporting reaction force for supporting is provided for the system by friction between the air pressure film and the hole wall; the settlement amount of the load plate is directly measured by a measuring sensor and in-hole load plate testing is realized.