Submicron alumina powder (SAP) was added into the green bodies of the architectural ceramic plates by preparation process of building ceramic plate. The effects of SAP on appearance, sintering properties and mechanical property of the ceramic plates were investigated. The results show that SAP is well dispersed in the ceramic bodies and improves the whiteness of ceramic plates effectively. The samples with the dosage of SAP below 15% (mass fraction) have a low water absorption of less than 0.1% and an increasing flexural strength. When SAP dosage is 15% （mass fraction）, the flexural strength of the sample reaches 96 MPa, which is 30% higher than that of the sample without alumina. The further increase in the dosage of SAP results in higher water absorption and lower flexural strength. In the low-quality raw materials with low whiteness, the whiteness and strength of the products can is greatly improved by adding submicron alumina powder, which can not only reduce the consumption of high-quality resources, but also better meet the requirements of decorative effect and mechanical properties of ceramic plates.