In this paper, we present a novel noise margin model of surrounding-gate MOSFET working on subthreshold CMOS logic gates. Based on the device physics and equivalent transistor model, theoretical analysis of noise margin for SRG MOSFET operating in low-voltage condition is revealed. It is shown that the device parameters such as the thick silicon thickness tsi, thick gate oxide thickness tox, short channel length Lg, and low supply voltage Vdd can severely degrade the noise margin NM. On the contrary, the small subthreshold slope induced by device parameters can suppress the NM degradation efficiently. Being similar to DIBL, NM degraded by the device parameters can also be uniquely determined and controlled by the scaling factor according to scaling theory.