The invention belongs to the technical field of nuclear assistant cooling water of mega-kilowatt nuclear power stations and discloses a novel grillage connection device for spent fuel pool expansion and a connection method of the novel grillage connection device for spent fuel pool expansion. The novel grillage connection device comprises a pair of grillage base plates and a pair of grillages andfurther comprises a connection assembly used for connecting the two adjacent grillage base plates. The connection assembly comprises a connection plate, a first locating plate, a second locating plate, temporary screws and final screws, wherein the first locating plate and the second locating plate are arranged at the two ends of the connection plate correspondingly, the temporary screws are usedfor installing the first locating plate on one grillage base plate, and the final screws are used for installing the second locating plate on the other grillage base plate. The first locating plate isinstalled on one grillage base plate through the temporary screws, the second locating plate is installed on the adjacent grillage base plate through the final screws, the first locating plate and the second locating plate are connected through the connection plate, and then connection between the two adjacent grillages is achieved. In this way, the stability of the grillages is guaranteed, and the grillages are prevented from toppling in an earthquake.