In order to develop formulations of paraffin wax/silane emulsion for wood modification, an orthogonal test was designed to determine the effect of alkoxysilane chain length and ratio of wax to silane. This test also studied hydrophile-lipophile balance（HLB） value and content of surfactant on stability and particle size of the paraffin wax/silane emulsion. Moreover, water repellent efficiency of wood samples treated with different paraffin wax/silane emulsions was also determined. The results indicated that the optimal emulsion formulation was found with 2∶1 ratio of wax to silane as well as 13.5 of the HLB value and 6% of the surfactant content. The emulsion reached stability grade 1 with 195.7 nm average particle size and 27.3% water repellent efficiency of the wood samples achieved after 384 h immersion.