Abstract: An in-situ method based on the actively heated fiber Bragg grating for monitoring dry density is proposed (abbreviated to H-FBG) to make a progress in the existing technique. The relationship between the temperature characteristic value (T_t) and the dry density (ρ_d) is established through the thermal conductivity for the in-situ monitoring of the dry density. A series of indoor tests are carried to verify the feasibility of the method, the effects of moisture content and types of soils are discussed, and the heating parameters are determined. The results show that T_t decreases with the increasing ρ_d, and it is described well using the exponential function. 15 W/m and 5 min can be the best heating parameters applied for the measurement. The temperature of the soils with a higher water content decreases slowly owing to the effects of micro-structure of soils. The results may provide the theoretical and technical foundation for the further application of the proposed method.