For the demand for large-diameter thick-walled seamless pipes of Sanicro25 steel for advaced ultra supercritical units(USC), a trial production of large-diameter thick-walled pipes with the specifications of Ф500 mm×Ф335 mm×3000 mm was conducted by Inner Mongolia North Heavy Industries Group Corp. Ltd. using a 36,000-ton vertical extruder. The surface quality of the steel pipes was excellent. Specimens extracted from the large-diameter thick-walled steel pipes were subjected to solution treatment at 1180 ℃ for 30 and 60 min respenctively, both of which demonstrated favorable comprehensive properties. Comparable performance indicators were achieved, including the yield strengths of 347.5 and 345.5 MPa, the tensile strengths of 735 and 730 MPa, the impact energies of 110 and 102 J, and the grain sizes of 4.5 and 4.0 grades The mechanical properties exceed the requirements specified for small-diameter pipe standards. The longitudinal mechanical properties and impact property of the large-diameter thick-walled pipes matched those of as-delivered small-diameter pipes.However, a significant discrepancy was observed between transverse and longitudinal impact properties,  which was attributed to the enhanced crack propagation resistance along the longitudinal fiber direction in steel pipe after extrusion.