The Fabry-Perot cavity（F-P cavity）is a widely utilized optical device with a multitude of applications，including those in astronomical detection，precision measurement，and sensor technology. At present，the conventional gas-gap Fabry-Perot cavity continues to be the preferred option for atmospheric detection and filtering applications. However，this type of cavity is subject to significant disadvantages，including a large volume and susceptibility to mechanical vibrations，which can have a detrimental impact on its performance. In contrast，the solid-gap Fabry-Perot cavity offers the potential for integration advantages that can effectively mitigate these issues. To guarantee the optimal filtering performance of the solid-gap Fabry-Perot cavity，a methodology for the precise determination of its cavity length is presented in this paper. By proactively regulating intrinsic hardware parameters，precise control of the filtering performance can be attained. This not only reduces the hardware size but also minimizes tuning-induced vibrations，thereby supporting the utilization of Fabry-Perot filter devices in spaceborne applications. A transmission spectral detection system is developed based on the aforementioned methodology，and the experimental tests are conducted on substrates. The results demonstrate that the system displays a fluctuation of 20 nm when measuring processing amounts at discrete points on the substrate. This method has successfully demonstrated initial precision in detecting the cavity length of the solid-gap Fabry-Perot cavity while confirming the feasibility of controlling its inherent parameters. Furthermore，the use of light feedback within an enhanced stabilization system enables the successful detection of an 8 mm thick substrate with clear transmission spectral lines，thereby highlighting the scheme's advantage in offering a broader detection range. This research establishes a fundamental basis for achieving precise control over filtering performance at the hardware level，which has the potential to facilitate accurate calibration of polishing removal quantities within existing polishing processes.