A warping harness is proposed to simply and efficiently correct low-order aberrations that occur during manufacturing and operation of a telescope. For the Thirty Meter Telescope (TMT) tertiary mirror, the issue to be solved by the warping harness is particularly challenging due to its complicated load conditions and limited mounting space. In this study, first, a new type of whiffletree-based warping harness configuration applied to a ¼-prototype TMT tertiary mirror is presented and optimized using finite element analysis (FEA) to improve the output precision of the moment actuator. Next, based on the new configuration, a simulation method for a correction process is proposed. The results show that the root mean square value of the mirror-surface error converged from 64.9 to 25.4 nm after correction, which satisfied the requirement document of TMT. Finally, combined with the analysis and calculation results, the moment actuator testing system with high-precision displacement-force-strain is established to assess the system errors. The tests of the moment actuator displacement, stress, strain-output precision, linearity, and repeatability are completed, and all errors were found to be within a controllable range. The results show the validity and feasibility of the designed warping harness, which can prove its applicability in more complicated conditions and, to a certain degree, broaden the application scope of the warping harness.