Reliable and timely data delivery, namely, real-time communication, is a key aspect for achieving the agile manufacturing goals of Industry 4.0. Moreover, reducing the maintenance, infrastructure and reconfiguration costs, and increasing the flexibility are general goals for communication systems in Industry 4.0. Although some works have extended the Ethernet standard IEEE 802.3 to satisfy the real-time requirements of industrial automation systems, the existing works have one or more of the following drawbacks: poor scalability, insufficient self-configuration capabilities, or increased costs due to their use of proprietary hardware. In this paper, we propose a Time-slotted Software-defined Industrial Ethernet (TS-SDIE) for real-time Quality of Service (QoS) in Industry 4.0. The paper addresses two key technologies of TS-SDIE, time synchronization and time slot-based packet switching. First, we develop a precision time protocol-based link delay compensation mechanism to handle the delay variance in networks. Precise synchronization is achieved at the microsecond level. Second, we design a system architecture for time slot-based industrial switches with four modules responsible for time synchronization, flow classification, time slot assignment, and packet forwarding, respectively. The experimental results show that the switch delay and its jitter can be reduced to 12.2μs and 0.12μs, respectively, for packets with a size of 100 B, which satisfies the requirements of time-sensitive networking for industrial automation systems.