Co-seismic strain changes of the Wenchuan Mw7.9 earthquake recorded with three four-component borehole strainmeters showed NW-SE and roughly EW extensions, respectively, at two locations in the interior and northern part of Tibetan plateau, and NS shortening at a location south of the epicenter, in agreement with the tectonic stress field of this region. The observed values of as much as 10-7 are, however, larger than theoretical values obtained with half-space and spherical-earth dislocation theories, implying the existence of other effects, such as local crustal structure and initial stress. Co-seismic strain changes of the Wenchuan Mw7.9 earthquake recorded with three four-component borehole strainmeters showed NW-SE and roughly EW extensions, respectively, at two interior in the interior and northern part of Tibetan plateau, and NS shortening at a location south of the epicenter, in agreement with the tectonic stress field of this region. The observed values ​​of as much as 10-7 are, however, larger than theoretical value obtained with half-space and spherical-earth dislocation theories, implying the existence of of other effects, such as local crustal structure and initial stress.