The invention provides a thin-wall planet carrier machining method and a tooling fixture. The thin-wall planet carrier machining method comprises the following steps: a reference hole and planet shaft holes in a first planet carrier body are subjected to rough machining and prevented from being machined into reach the finished size; planet shaft holes in a second planet carrier body are subjected to rough machining and prevented from being machined into reach the finished size; a spline hole is machined to reach the finished size; after the planet shaft holes in the first planet carrier body and those in second planet carrier body are aligned, the first planet carrier body and the second planet carrier body are welded together; a welded workpiece is placed on the tooling fixture; the centering operation is performed by utilizing the matching between a core shaft and the spline hole; and after the workpiece is clamped, the reference hole and the planet shaft holes are machined to reach the finished size at a time. By adoption of the thin-wall planet carrier machining method provided by the invention, the clamping mode and the clamping reference are changed; after the positioning and the compaction, the reference hole and the planet shaft holes are machined at a time, so that the position degrees of the reference hole and the planet shaft holes can be guaranteed; and accordingly, the circumstance that the assembly quality is influenced and the defective rate of parts is greatly lowered due to the unqualified positions degrees caused by accumulative errors can be avoided.