Foam concrete has two major shortcomings resulting primarily from pore structure: high drying shrinkage and weak frost resistance. This article reports on a study of how various water-cement ratios affect high drying shrinkage and weak frost resistance. Stereomicroscopy, acoustic wave, and nitrogen adsorption methods measured macroporous and microscopic pore structures to analyze drying shrinkage and frost resistance mechanisms. Drying shrinkage was shown to gradually increase as water-cement ratios increased from 0.4 to 0.7. This can be attributed to increased water loss via capillary holes and greater capillary tension. Frost resistance maximized at a water-cement ratio of 0.5. As the water-to-cement ratio increased from 0.4 to 0.5, accessible pores with an average size of 10–50 nm increased. The volume of harmful 50–200-nm pores and pores larger than 200 nm increased. When water-cement ratios increased from 0.5 to 0.7, the number of 0–200-μm pores decreased sharply, whereas pores larger than 400 μm increased dramatically.