Length is one of the seven basic physical quantities, which is widely used in people′s work and life. In this paper, a two-arm laser ranging system composed of two laser ranging sensors is proposed. It can measure the distance between the instrument and any point in space and between any two points in space in a non-contact way. It also has the function of measuring internal angle, external angle and two-dimensional perpendicularity. The measurement error of the system is analyzed theoretically and simulated by MATLAB software. The actual experimental test shows that the absolute error can be controlled within 1 mm when the measurement distance is less than 1 m, and the relative error can be controlled within the order of 1‰ when the measurement distance is less than 50 m. And the repeatability measurement experiment and measurement uncertainty evaluation verify the error index of the system, and point out the direction for the system improvement. The instrument also has the advantages of low power consumption, low cost and easy portability, so it has broad application prospects.