Environmental education is an important task conducted in schools at all levels, from preschool to university. This study uses a systematic review of the existing literature to analyze the status quo of pre-service preschool teachers' environmental competencies and the strategies for approaching environmental education in preschool teacher training. There were 14 studies selected by inclusion criteria and rigorously analyzed. These literatures provide an overview of the studies performed to date and allows for a more comprehensive understanding of some formal aspects of the research problem. Most of the reviewed studies measured pre-service preschool teachers' environmental education competencies (N = 8), while a few studies (N = 6) focused on the approaches of pre-service training programs in environmental education, identifying three strategies: (1) addition of environmental education courses in the program, (2) a separate course in environmental education methods, and (3) integration of environmental education methods into courses in existing programs. The search results show that environmental education in preschool teacher training is a recently emerged topic with a scarcity of studies. The findings emphasize the need for a detailed evaluation of current preschool teacher training programs to establish program development strategies regarding environmental education. In addition, this review calls for future research that focuses on experimenting with and applying environmental education strategies in preschool teacher training programs.