【Objective】 To explore the plasma-activated medium (PAM) produced by low temperature plasma (LTP) on the proliferation and angiogenesis of human umbilical vein endothelial cells (HUVECs) so as to provide theoretical basis for the future use of PAM to promote wound healing and inhibit tumor angiogenesis. 【Methods】 HUVECs were selected as the in vitro research model. The PAM-containing medium after LTP treatment for different time points (0 s, 15 s, 30 s, 45 s, 60 s, and 75 s) was used for intervention. The influence of PAM on HUVECs viability was assessed using the MTT assay and cell cycle analysis. The effects of PAM on angiogenesis were examined through angiogenesis experiments. Intracellular levels of reactive oxygen species (ROS) were measured using fluorescence probes. A melanoma mouse model was established, and CD31 expression was detected by immunohistochemistry. 【Results】 As the treatment time increased, the intracellular levels of ROS also elevated. PAM derived from LTP exhibited a bidirectional effect on angiogenesis in HUVECs. Compared to the control group (0 s), low-dose treatments (15 s and 30 s) enhanced HUVECs viability, while high-dose treatments (45 s, 60 s, and 75 s) significantly decreased cell viability (P<0.05). The proportion of HUVECs in the S phase was significantly increased in the PAM-15 s and PAM-30 s groups, but markedly decreased in the PAM-45 s, PAM-60 s, and PAM-75 s groups, with statistically significant differences (P<0.05). The HUVECs tube formation ability was enhanced in the 15 s and 30 s PAM groups, but diminished in the PAM-45 s, PAM-60 s, and PAM-75 s groups, characterized by the decreased numbers of vascular nodes, intersections, meshes, and branching points (P<0.05). After PAM treatment in the melanoma mouse model, the control group exhibited widespread distribution of CD31 in tumor tissue, while the PAM-5 min and PAM-10 min groups displayed reduced distribution of CD31. 【Conclusion】 Short-term exposure to PAM enhances HUVECs proliferation and angiogenesis, whereas prolonged exposure suppresses cell viability and inhibits angiogenesis.