This work reported the effect of welan gum (WL) on stabilizing the foam of hydroxypropyl methylcellulose (HPMC), which compared to konjac glucomannan (KGM) and guar gum (GG). The effects of total concentration and ratio on the foaming properties of the HPMC/WL composite system were studied systematically through the analysis of foaming capacity, foam stability, foam morphology at the macro and micro levels, rotational rheology properties, interface rheology properties, and microstructure. Finally, the interaction forces, conformation, distribution, and rearrangement of HPMC/WL molecules on the interface were speculated to elucidate the stability mechanism. The experimental results showed that when the concentration was 1%, and the ratio of HPMC/WL was 8:2, the foaming capacity was the maximum, reaching 586.66%; when the total concentration was fixed at 1%, the ratio of HPMC/WL was 2:8, the foam stability reached 96.507%. The excellent shear-thinning ability of WL was one crucial factor for the excellent foaming properties of HPMC/WL composite. The high apparent viscosity significantly improved the foam stability of HPMC/WL composite, which was mainly caused by the physical interaction between HPMC and WL molecules after whipping. In addition, the composite foam of HPMC/WL after vacuum freeze-drying presented a porous, dense, and uniform cellular structure. This study expanded the application of WL as a stabilizer for a heterogeneous system and raw material for the carrier of bioactive substances in the delivery system.