Using a heavy-metal (HM) alloy layer in spin-orbit torque (SOT)-based devices is an effective method for obtaining a high current-spin conversion efficiency θ SH . In this work, SOT-based spintronic devices with a Pt 100- x Ru x -alloyed HM layer are studied by applying harmonic Hall measurements and magneto-optical Kerr effect microscopy to detect the θ SH and to observe the process of current-induced magnetization switching. Both the highest θ SH of 0.132 and the lowest critical current density ( J c ) of 8 × 10 5 A/cm 2 are realized in a device with x = 20, which satisfies the high SOT efficiency and low energy consumption simultaneously. The interfacial Dzyaloshinskii-Moriya interaction can be overcome by increasing the in-plane assist field. Meanwhile, the minimum in-plane field required for current-induced complete switching can be reduced to ±60 Oe. Our study reveals that using the Pt-Ru alloyed HM layer is an effective route for SOT application with enhanced performance.