The quality, performance, and morphology of Mg-Gd-Y-Zr alloy regulated short circuit (Fronius CMT) welding components is directly depend on whether the droplet transfer process is stable. However, due to the inherent properties of the material, Mg-Gd-Y-Zr alloy is highly sensitive to heat input, and prone to spattering in the process of droplet transfer. In this work, three types of spattering were observed through high-speed cameras, which are caused by internal burst of droplet, wire withdrawal, and repelled transfer. Causal relationship of spattering mechanism and process parameter was explored especially in the stage of wire melting and droplet growth, and a simplified numerical model was used as an auxiliary means to further reveal the spattering of repelled transfer. The result indicated that the recoil pressure of metal vapor is the vital factor which destabilize the shape and motion trajectory of droplet and eventually caused spattering. The range of the process parameter for achieving a stable droplet transfer and well-formed weld bead is relative narrow which the peak current is recommended between 150 A to 170 A, and peak duration around 7 ms.