Introduction: Patients with chronic non-specific low back pain (CNSLBP) were found with impaired postural control in previous studies. Since the trunk muscle take important efforts on core stability, the study aimed to examine the relationships of postural control during stance tasks and the contractility of trunk muscle in young adults with CNSLBP and without. Methods: Healthy individuals (n = 25) and individuals with CNSLBP (n = 30) were included. The thickness of the bilateral transversus abdominis (TrA) and lumbar multifidus (MF) was measured during rest and maximal voluntary contraction, and the change percentages (TrA%, MF%) were calculated. Regarding postural control, COP path length and sway area during the stance tasks were measured thrice in each group. Results: The bilateral TrA% of the CNSLBP group was less than that of the HC group (p < 0.05). The bilateral TrA% of the CNSLBP group was less than that of the HC group (p < 0.05). The bilateral MF% showed no significantly different(p > 0.05) between the two groups. Compared with healthy controls, CNSLBP patients resulted larger path length and sway area of COP during most of static stance tasks. During the EO task in the CNSLBP group, TrA% was found correlate to COP path length (p < 0.05); the right MF% was correlated with COP sway area (p < 0.05). No significant correlations appeared in the healthy controls (p > 0.05). Conclusions: Compared with healthy individuals, impaired postural control during static stance with eyes open in patients with CNSLBP was likely to be related to the poor contraction ability of bilateral transversus abdominis and correlated to the normal contraction ability of right lumbar multifidus.