Orthogonally linearly-polarized lasers and its new applications in precision measurement are presented, including: 1) orthogonally linearly-polarized lasers, 2) principle for laser nanometer ruler (displacement sensor based on the competition between two polarized lights of the frequency splitting lasers), 3) principle for phase retardation measurement using frequency splitting technology, 4) principle for phase retardation measurement based on laser feedback effects. These novel principles have remarkable characteristics of simple structure, tracing back to optical wavelength. The laser nanometer ruler has been applied in practical occasions, and its performance is as follows: the measurement range 12 mm, resolution 79 nm, and linearity less than 5×10^-5. The repeatability reaches 0.3′ for phase retardation measurement system based on frequency splitting technology. However, laser feedback phase retardation measurement system has the advantage of on-line measuring.