The development of an in-line digital microholointerferometer for micromechanical testing is presented. With respect to the specific requirements on the microscopic scheme in micromeasurement, the application of a long-distance microscope is introduced with emphasis. A critical issue, validation of the developed system, is addressed. Aided by finite element analysis and analytical calculation, experimental measurement with the system is examined using a hybrid approach. To evaluate the performance of the system, a microbeam experiment is presented. Results measured with the system, as well as the numerical simulations, are obtained. Quantitative comparisons are carried out in terms of load-induced variations of the test sample, based on which the conclusions are given.