A lean-premixed swirling combustor with synthesis gases is studied in non-reacting and reacting cases using large-eddy simulation. Code validation and grid dependence test are performed to validate the models and mesh resolution. With the introduction of unmixedness and correlation coefficients in the non-reacting cases, the influence of Reynolds number on recirculation, vorticity breakdown and mixing is studied. In reacting cases, instant and time-averaged scalar fields are examined to study the flame dynamics for a varied fuel composition and operating conditions. The results reveal the effects of hydrogen concentration, Reynolds number, equivalence ratio and pressure on the combustion processes. Conclusions for syngas combustion operation from this work are expected to provide useful information for gas turbine combustor design.