The invention discloses a swing type support frame for a FMT800T numerical control double-tool-post crankshaft main shaft neck lathe on a car crankshaft full-automatic production line. The swing type support frame comprises a rotating shaft driven by a power oil cylinder mechanism; an extension rod and a support plate driven through a gear rack mechanism are arranged at the end of the rotating shaft; a shell connected with the gear rack mechanism is connected with the end of the tubular extension rod; the tubular extension rod coats the outer side of the rotating shaft; a movement decomposition mechanism is arranged between the other end of the tubular extension rod and the rotating shaft for decomposing rotation of the rotating shaft to up-down linear movement and rotation of the extension rod; and the linear movement and the rotation are respectively acted. When a crankshaft is turned and clamped, the support plate for supporting the crankshaft can firstly shrink back, and then rotates by 90 degrees; and the support plate is guaranteed to be far from the crankshaft, so that no influence is generated on machining of the crankshaft. After a crankshaft machining machine tool is provided with the device, the working efficiency can be improved, and no damage of the crankshaft from iron chips during machining is guaranteed.