The invention discloses a rigid plugging agent for a drilling fluid and a preparation method of the rigid plugging agent. The rigid plugging agent comprises the following components in parts by weight: 2-6 parts of walnut shells, 2-7 parts of calcite, 0.8-2.4 parts of sawdust, 1-2 parts of polypropylene fibers and 1.2-2.7 parts of elastic particles. The invention also provides a preparation methodof the rigid plugging agent. The rigid plugging agent and the preparation method thereof effectively overcome the problems of poor pressure bearing capacity and plugging effect, proneness to leakage,high production cost and low cost performance of conventional plugging agents.