Different from conventional wired line connections, industrial control through wireless transmission is widely regarded as a promising solution. However, mission-critical applications impose stringent quality of service (QoS) requirements that entail ultra-reliability low-latency communications (URLLC). The primary feature of URLLC is finite blocklength (FBL), and conventional Shannon Capacity is not applicable. In this paper, we consider URLLC in a factory automation (FA) scenario, where wireless signal are easy to be blocked by densely deployed machines. To address this issue, we propose to deploy intelligent reflecting surface (IRS) to create an alternative transmission link when the direct link is blocked, which can enhance the transmission reliability. We focus on the performance analysis for IRS-aided URLLC-enabled communications. Both the average data rate (ADR) and the average decoding error probability (ADEP) are derived and asymptotic analysis is performed to obtain more design insights. Extensive numerical results are provided to verify the accuracy of our derived results.