The invention discloses a double loop network-based protection device free of a main in-situ transformer and a protection method. The double loop network-based protection device free of the main in-situ transformer comprises in-situ protection sub-machines, which are arranged at a high-voltage side, a medium-voltage side and a low-voltage side of a transformer respectively; the protection sub-machines are in hand-in-hand connection through double loop networks; each protection sub-machine collects the analogue quantity and the switch quantity of the side in situ, and is in bidirectional communication with the other protection sub-machines through the double loop networks to share data; each protection sub-machine comprises the same main and backup protection-integrated protection module for the transformer; a circuit breaker is arranged between each protection sub-machine and the side of the transformer; and each protection module trips off the corresponding circuit breaker according to the set backup protection action conditions and differential protection action conditions. By the double loop network-based protection device free of the main in-situ transformer and the protection method, the problem that a host of an existing protection device with the main transformer cannot be installed in situ is solved; and furthermore, multiple sets of differential 'conjunction gate' logics are adopted by the protection device, so that the protection reliability is improved.