The invention provides a method for estimating the thick-wall thinning reliability of a hollow mandril. The method comprises the following steps of: (1) setting simulation conditions; (2) simulating the radial pressure stress suffered by the hollow mandril in the using process; (3) calculating the radial pressure of the hollow mandril; (4) setting a safety coefficient; (5) comparing the simulatedpressure and the calculated pressure; and (6) thinning the hollow mandril through processing. The invention has the effects that: the method can be used for effectively carrying out reliability estimation on the hollow mandril with any wall thickness, so as to solve the difficulty that the thick-wall thinning degree of the hollow mandril is difficult to the controlled. The method disclosed by theinvention brings a reliable basis for design and use of the hollow mandril, design and use risks of the hollow mandril are reduced, the utilization rate of the hollow mandril is erected to the maximum extent, the production efficiency of a seamless steel pipe can be greatly improved, and the production cost is reduced; and the method makes a contribution to development of low-carbon and environment-friendly industry.