Abstract: This study aims at integrating the observational data recorded by borehole volume strainmeters and component borehole strainmeters on the area strain basis. This is helpful for current data evaluation, data processing and analysis, and earthquake prediction. Based on the Pan-Chen model (Pan; Chen and Yang), Evertson theory and theory of elasticity, both volume strain and area strain models were set up under area stress. In addition, we have derived similar formulas for calculating transform coefficient between volume strain and area strain in observation hole, empty hole and non-porous rock condition, respectively. The difference only lies in the factor k (ratio of volume strain gauge on the steel cylinder wall or non-porous rock surface strain to area strain of the empty hole rock). The theoretical formula derived from Evertson model is close to the case of empty hole rock with the rock elastic modulus ranged from 4times;1010 Pa to 8times;1010 Pa. Both results may be regarded as a simplified Pan-Chen model. For non-porous rock, the factor k may be predicted by taking rock modulus as 1times;1010 Pa. This paper discussed some factors related to transform coefficient based on real observation data.