MTS815.04 testing system is one of the most excellent equipments in the field of current rock mechanics testing research for its outstanding loading system, controlling system and measurement system. Based on the principle of extensometer measurement in axial deformation and lateral deformation configured by MTS system, some questions on postpeaking strength curves emerged from applications of deformational measurement techniques are reasonably interpreted. Firstly, the original lateral strain calculation methods are improved on the basis of the original chaining type of lateral extensometer measurement techniques. Some problems on axial deformation measurement method are discussed and the improved method is put forward. At last, a type of extensometer calibration technique for deformation sensor is proposed. All the measurement technical improvements can provide testing condition and guarantee for laboratory rock mechanical testing research.