Abstract: A contact signal acquisition circuit for online checking a gas density relay on site is provided, including a first connecting circuit, connecting a contact of a gas density relay to a contact signal control loop, and a second connecting circuit, connecting a contact of the gas density relay to a contact signal sampling interface of an online check device. In a non-checking state, the second connecting circuit is disconnected, and the first connecting circuit is closed; and in a checking state, the first connecting circuit is disconnected, and the second connecting circuit is connected, so as to connect the contact of the gas density relay to the contact signal sampling interface of the online check device, guaranteeing that no contact action signal is uploaded during checking and safe operation of a power grid is not affected.