Assessment of formaldehyde (HCHO) removal using constructed wetlands (CWs) was scarcely ever reported. Here, the feasibility of HCHO removal was studied in tidal flow CWs (TFCWs) with/without wetland vegetation (Canna indica L.). The HCHO removal efficiencies of TFCWs with various initial loads (25, 50, 75, and 100 mg L^-1) were investigated, then the impact of influent pH and DO values on HCHO removal was evaluated. Results showed that microbiological degradation was the main HCHO removal pathway. The aerobic condition (DO concentration >4 mg L^-1) and neutral/weak alkaline pH (approximately 7-8) was favorable for the HCHO removal. In order to upgrade the HCHO removal potential, a two-stage cyclic CW (t-TFCW) was designed. For an influent HCHO concentration around 100 mg L^-1, t-TFCW showed a stable and efficient HCHO removal performance, where the average HCHO removal rate was found to be 98.1% after a 6- hour treatment.