This paper studies integrated process planning and scheduling (IPPS), a typical workshop scheduling problem, and mainly investigates the uncertain problems in the actual industrial production process. Then, we introduce the theoretical knowledge of interval numbers and adopt the interval number comparison method. Specifically, interval numbers are used to replace the determined processing time, and uncertain IPPS problems are modeled based on the interval number theory. Based on this, a hybrid particle swarm algorithm is proposed to solve the uncertain IPPS. Meanwhile, the genetic operator is introduced to improve its ability to deal with combined optimization problems. The above theoretical results are applied to the process planning and scheduling of a mechanical workshop, thus verifying the effectiveness of the proposed method.