Abstract: Analyzing the influence of the temperature gradient,air disturbance,vibration and drift error on the measurement accuracy of the long trace profiler (LPT),a stable system was designed for the LPT,that body made mainly with double deck Aluminum alloy material and a closed shield structured with interlayer water cycle cover.To improve the stability of the system,several measures were introduced,for example,designing the closed structure and increasing solder joints of the interlayer to reduce the influence of air disturbance;selecting Aluminum alloy materials with good thermal conductivity and circulating water system to improve the temperature stability;taking the graphite thermal film for the inner wall paste to avoid local excessive temperature rise and improve the temperature distribution uniformity.The ANSYS software was used to check the structural strength of the stable system,optimize the distribution of solder joints,and further improve the structural stiffness.The actual tests of the K-B mirror samples show that,the measurement accuracy of the LTP device with stable system is higher and less noise for surface shape measure.Performance test of the self collimator installation shows that,the noise of autocollimator with stable system can be efficiently suppressed,greatly improve the detection performance.