The utility model discloses a full-thickness sampler for wet crude oil of an oil tank truck. The full-thickness sampler is designed to sample the crude oil in various sections in a tank of the oil tank truck. The lower end of a sampling barrel of the sampler is connected with a check valve housing; a low-density valve clack that is fixed by a hinge, and can rotate around the hinge by 90 degrees is arranged in the check valve housing; and a seal ring is arranged at the upper end of a bottom hole of the check valve housing. In a sampling process, the sampler is placed in liquid in the tank of the oil tank truck perpendicularly; the low-density valve clack is opened immediately after being contacted with a liquid level; the wet crude oil in various sections enters the sampling barrel uniformly; the sampler is lifted upward after sampling is accomplished; the low-density valve clack is closed immediately by liquid flow resistance, and sealed by the seal ring; wet crude oil samples in various sections can be taken out from the tank of the oil tank truck by the sampler once; the representativeness of the samples is good; the sampling frequency is low; and the sampler is easy and simple to operate.