Until now, few epidemiological studies have focused on the association between ambient particulate matter (PM) pollution and hospital outpatient visits for overall and cause-specific respiratory disease, especially in Lanzhou. This study aimed to evaluate the short-term effects of PM_2.5, PM_C, and PM₁₀ on hospital outpatient visits for overall and subtypes of respiratory disease in Lanzhou, China, during 2007–2017, using a generalized additive model (GAM). We further assessed the impact of ambient size-fractioned PM on daily total and cause-specific respiratory morbidity, following a series of air quality improvement action in the area with overall and period-specific analyses. Positive associations were identified between PM_2.5, PM_C, and PM₁₀ and daily morbidity rates from overall respiratory diseases, upper respiratory tract infection, lower respiratory tract infection, pneumonia, and COPD at different lag pattern. Each 10 μg/m³ increase in PM_2.5 at lag07, PM_C at lag03, and PM₁₀ at lag06 corresponded to an increase of 1.353% (95% CI: 1.249%, 1.457%), 0.052% (95%CI: 0.015%, 0.089%), and 0.201% (95% CI: 0.165%, 0.236%) in daily hospital outpatient visits for total respiratory, respectively. We did not find significant effects of PM_2.5, PM_C, and PM₁₀ on asthma. For specific subtypes of respiratory diseases, the effects of PM were strongest on pneumonia morbidity, with an increase of 3.712% (95% CI: 3.308%, 4.117%), 0.874% (95% CI: 0.698%, 1.051%), and 0.967% (95% CI: 0.836%, 1.099%) per 10 μg/m³ increment in PM_2.5, PM_C, and PM₁₀, respectively. The exposure-response association was non-linear across the full range of exposures. With drastic reductions in annual PM levels, the three size-specific PM associate and respiratory morbidity risk showed decreasing trend over time. This study suggests that PM could exert adverse influences on the outcomes of all-cause and cause-specific respiratory outpatient visits in Lanzhou, China. PM_2.5 would have significant effects on pneumonia and RTI. Strategies should be considered to further reduce levels of ambient PM_2.5.