• The film prepared under an electric field provided extremely fluffy morphology. • The film prepared under combined electric/magnetic fields revealed denser morphology. • Dense/porous double-layer WO 3 films were designed and fabricated by sparking method. • The reversibility has been improved from 16.1% to 83.7%. • Enhanced 7-fold optical modulation and 9-fold coloration efficiency. This article reports on the morphological design to enhance reversibility and electrochromic performance of porous WO 3 films synthesized by sparking method using electric field (E = 6 kV/cm) and magnetic field (B = 500 mT). The excellent H + ion exchange between liquid electrolyte and the WO 3 films was influenced by extremely fluffy morphology as observed by sparking under an electric field— WO 3 with E sample. The morphology of the films becomes denser when sparked under a combination of electric and magnetic fields—WO 3 with (E + B) sample—which reduces the diffusion pathway and improves electron transfer within the films. Finally, we designed and fabricated dense/porous double-layer WO 3 films (WO 3 with (E + B)/E sample) to integrate their advantages to enhance 7-fold optical modulation and 9-fold coloration efficiency. Furthermore, the reversible efficiency increased from 16.1 % to 83.7 % compared to WO 3 with E sample.