China’s protected horticulture largely depends on soils as growth medium with low to medium technology, which is characterized by high input, high output, and intensive soil use. The cultivation area of the protected horticulture was 2.67 million hm2 in 2021, accounting for more than 80% of the global protected horticulture area. However, the protected cultivation resulted in soil degradation, non-point pollution, increased greenhouse gas emissions, and loss of crop yield and quality. This study focused on soil sustainability in protected horticulture. It summarized the obstacles that limited the sustainability of protected horticulture, which were the imbalance of soil nutrients, low soil environmental quality, the penalty of crop yield and quality, and backward land management and policy. These obstacles were mainly attributed to the low accuracy of plastic greenhouse environmental control and fertilization caused by low technology of protected facility, soil continuous cropping obstacles induced by inappropriate fertilization and monocropping, and less integrative innovation on soil management technology due to the lack of suitable land policy. This study proposed seven strategies to address current soil unsustainability, including soil profile design when building a plastic greenhouse, soil remediation at the fallow period, plastic greenhouse environmental regulation, control of soil input, buildup of crop rotation mode, plant resistance improvement, and the adaptation of land use policy. These strategies are expected to provide reasonable and scientific foundations for sustainable soil management in plastic greenhouses of low-to-medium technology possessed by smallholders.