In this paper, we propose an ultra-thin spoof surface plasmon polaritons (SPPs) structure, periodically loaded with trapezoidal grooves. Compared to the reported SPPs with rectangular grooves, the proposed SPPs structure can support the guided surface SPP wave with enlarged propagation constant, which implies an enhanced confinement of surface wave along the spoof SPPs structure. Guided-wave characteristics of the proposed SPPs structure are theoretically investigated by virtue of a numerical short-open calibration (SOC) technique. The results show that the loss of spoof SPPs is lower than that in other reported spoof SPPs structures. Experiment on prototype in microwave frequency regime is carried out which validates the theoretical findings. It is believed that the proposed structure could be scaled to THz frequencies, and is very promising in developing the miniaturized planar surface plasmonic devices and circuitry.