This paper is to explore the applicability of coarse-grained argillaceous sandstone with strong expansibility as subgrade filler for high-speed railway in Western Liaoning Province. Under the condition that the conventional test method is limited, the limitation of the test method can be overcome by improving the test instrument, with the no-load expansion rate test, expansion test and California bearing ratio (CBR) test to be carried out for the coarse-grained argillaceous sandstone after the cement improvement. The results show that the addition of cement helps to obviously inhibit the expansion of coarse-grained argillaceous sandstone, with the optimal mass fraction of cement being 6%. Meanwhile, the CBR value of the subgrade filler increases from 2.6 of the original soil to 11.2 after improvement, with the strength increasing by about 331%.