Nonpharmacological management plays a key role in enhancing the quality of life for individuals with chronic obstructive pulmonary disease (COPD), asthma, or both. However, disparities in their physical, mental, and health empowerment outcomes have not been fully explored, particularly in relation to the moderating effect of eHealth literacy. This study aims to assess these disparities and examine how eHealth literacy moderates them to guide the development of tailored nonpharmacological strategies. We analyzed data from 2 waves of the nationally representative "Psychology and Behavior Investigation of Chinese Residents" surveys to identify participants who self-reported asthma, COPD, or both. We assessed 5 physical outcomes (quality of life, physical activity, sleep quality, appetite, nicotine dependence), 4 mental outcomes (anxiety, depression, perceived stress, resilience), and 3 health empowerment measures (social support, self-efficacy, eHealth literacy). Multiple regression with Holm-Bonferroni corrections revealed health disparities and the moderation effect of eHealth literacy. This unfunded study enrolled 1044 participants between June 2022 and August 2023, with data analysis completed within 7 months following data collection. The sample included 254 (24.3%) participants with asthma, 696 (66.7%) participants with COPD, and 95 (9.1%) participants with both conditions. The mean age of the participants was 48.61 (SD 19.70) years, and 536 (51.3%) participants were male. Linear regression showed that individuals with both COPD and asthma had lower health-related quality of life and higher anxiety and depression compared with those with either condition alone (b ranges from -0.15 to 3.35). This group also showed higher nicotine dependence than asthma-only (b=0.88) and lower resilience than COPD-only groups (b=-0.76) (all adjusted P<.05). eHealth literacy significantly moderated the effect of the disease group on all outcomes except physical activity (all adjusted P for interaction <.05). Nine disease pairs showed disparities in both eHealth literacy groups, 4 only in high literacy, and 8 only in low literacy (all P<.05). Individuals with both COPD and asthma had poorer quality of life, greater anxiety and depression, higher nicotine dependence, and lower resilience, underscoring the need for integrated psychosocial and behavioral interventions. Although higher eHealth literacy was associated with improved quality of life, sleep quality, and resilience, it also widened disparities in anxiety and depression. Therefore, while enhancing eHealth literacy may help reduce overall health inequities among patients with chronic respiratory diseases, its potential adverse effects on mental well-being warrant careful attention. Moreover, lower eHealth literacy was linked to more pronounced disparities, indicating that outreach efforts and digital resources should be specifically designed to reach and empower vulnerable populations. Overall, our findings advocate for condition-specific, eHealth-enhanced care pathways that not only foster digital literacy but also integrate comprehensive mental health services, thereby mitigating health disparities among individuals with chronic respiratory diseases.