The properties of green space for physical and mental health have been widely demonstrated, especially after the COVID-19 pandemic. However, few studies have systematically focused on spatial indicator thresholds that provide a sense of refuge with restoration benefits. Four morphological indicators as area, coverage, enclosure, and the ratio of width to height(D/H), were quantified for thirty-one scenes in outdoor green sheltered spaces in seven urban parks of Harbin in China. The results show that the sense of refuge and the morphological character of a green space constitute elements that influence restorative properties. Green spaces with different morphological indicators have different restorative properties. The morphological indicator ranges that produce better restorative properties were obtained: 250–500 m² for area, 0.25–0.35 for coverage, 0.3–0.4 or 0.8–1 for enclosure, and 0.7–1.5 for D/H. This can provide references for the construction of restorative activity spaces in urban parks.