Abstract: Synthetic microorganisms (genetically modified, altered, and reconstructed microorganisms) have great application potential in biological manufacturing, disease diagnosis and treatment, and environmental remediation. However, their large-scale application may pose environmental biosecurity risks and may lead to unpredictable consequences such as species invasion, loss of biodiversity, and ecosystem disruption. This paper summarizes the potential biosafety risks associated with the environmental release of synthetic microorganisms, discusses the environmental defense and detection technologies established by synthetic biology, and provides prospects for better mitigating the environmental risks of engineered microorganisms. The main findings are listed as follows. (1) Environmental Risks: The release of synthetic microorganisms can lead to environmental biosecurity hazards, horizontal gene transfer, niche occupation and ecosystem damage. These risks are primarily associated with the characteristics of modified synthetic microorganisms and the foreign genetic material they carry. (2) Mitigation Technologies: Technologies such as nutrient-deficient or environmentally sensitive microorganisms, gene circuits, the use of unnatural elements, and restricting the heterogeneous replication of plasmids can prevent the survival of synthetic microorganisms or the spread of nucleic acids in the environment. (3) Detection Methods: Specific detection methods for synthetic microorganisms, including molecular markers, biosensors, rapid nucleic acid detection, and general detection technologies such as microbial barcodes and high-throughput sequencing, can be utilized for environmental tracking of synthetic microorganisms. Future research directions include: (1) Biostorage Strategies: Upgrading efficient and stable biostorage strategies to cope with the rapid evolution of microorganisms. (2) Environmental Viability Analysis: Analyzing the environmental viability of synthetic microorganisms and assessing their potential risks through classification. (3) Interaction Mechanisms: Studying the interaction mechanisms between synthetic microorganisms and environmental organisms and their impact on the latter. (4) Environmental Abatement Technologies: Developing technologies to ensure the efficient removal of synthetic microorganisms after uncontrolled release.