Compared with the conventional broadside imaging mode used in traditional low-frequency radar, the high squint mode of airborne terahertz Synthetic Aperture Radar(SAR) can fully exploit its advantages of high-resolution and high-frame-rate, enables high-definition dynamic imaging of the forward squint area and significantly expands the platform's dynamic sensing range. In the broadside mode, terahertz SAR can achieve a larger Doppler bandwidth with a smaller aperture, resulting in relatively small range migration and comparatively simpler imaging processing. However, in the high squint mode, the increase in aperture length and the highly space-variant characteristics of range migration greatly raise the difficulty of motion compensation. To address this issue, this paper investigates high-squint terahertz SAR imaging techniques, employing a joint estimation method using system parameters and echo data to achieve high-precision motion parameter estimation and motion compensation. Based on airborne terahertz radar measured data, high-resolution imaging is achieved at a squint angle of 70°, with a resolution better than 0.2 m. Compared with conventional imaging methods, the proposed imaging algorithm achieves a reduction in Peak Side Lobe Ratio(PSLR) of 16.53 dB and a reduction in image entropy of 39.9%.