The invention discloses a liquid nitrogen freeze dryer direct-expansion cold trap. A cold trap box body is provided with a vacuum pumping port, a middle separation valve, a liquid nitrogen inlet and a nitrogen gas outlet, wherein a coiler fixed bracket and a coiler are arranged inside the box body, a convergence cavity, a tube nest and a convergence tube are also arranged inside the box body, thelower part of the tube nest is connected with the convergence tube, the upper part thereof is connected with the convergence cavity, the coiler is divided into an upper coiler and a lower coiler, anupper coiler inlet is directly connected with the convergence cavity, a lower coiler inlet is connected with a bushing on the tube nest, the convergence tube is connected with the liquid nitrogen inlet, and a nitrogen gas discharging pipe which is connected with the nitrogen gas outlet is lead out from the middle part of the upper and the lower coilers. The liquid nitrogen freeze dryer direct-expansion cold trap enlarges the freezing temperature range, and can improve the temperature homogeneity and heat exchanging efficiency of the cold trap.