The invention discloses an antitheft tree-pit bottom support plate system capable of effectively preventing freezing in winter and relates to the technical field of plant maintenance devices. The system comprises two support plate bodies. Each support plate body comprises several integrated vertical plates. Several horizontal plates are arranged at intervals between each two vertical plates, and the horizontal plates are arranged at intervals along the forward and backward direction of the support plate body. The horizontal plates on a same straight line are connected together through a connecting rod. The horizontal plate which is opposite to a rectangular gap and positioned at the outmost side is provided with a gap. The horizontal plates with the gaps are fixedly connected to the vertical plates. The two support plate bodies are connected as a whole through auxiliary locking members and a U-shaped lock. The front and back auxiliary locking members are connected through a connecting vertical bar. The system can effectively prevent inconvenience of too much water in the tree pit for pedestrians, can effectively prevent freezing in winter, has a certain antitheft effect, and is convenient to remove garbage at the bottom of the tree pit.