In order to quantitatively assess the solar stray light suppression capability of the heliospheric imager, a testing approach and experimental validation were investigated. In this paper, we proposed a method to test the solar stray light suppression capability of the heliospheric imager under laboratory circumstances by conducting segmented tests of the front-end baffle and the camera. This approach circumvented the issue that the structural scattering caused by the test under vacuum conditions would be overly large and influence the accuracy of the test results. The proposed method was then employed to assess the effectiveness of a heliospheric imager in suppressing solar stray light under laboratory conditions. The experimental results indicate that the PST of the front-end diaphragm of the heliosphere imager is 1.4×10^-8 at WACH1 and 4.3×10^-9 at WACH2. The error analysis of the test results reveal that the random error is 21.6%, and the PST resulting from the sum of system errors is 1.1×10^-8 at WACH1 and 4.2×10^-9 at WACH2. The test accuracy meets the requirements, demonstrating the feasibility and accuracy of the test method. The study presented in this paper offers a novel means to test the solar stray light suppression capability of heliospheric imager.