Laser-cooled 87Rb atoms are loaded from free space into anti-resonant hollow-core fibers ( AR-HCF) using a dipole trap generated by an 852 nm laser. We propose a theoretical model of the optical depth of atomic ensemble inside hollow-core fibers. The resonant optical depth ( ODres ) is obtained by fitting the transmission spectrum with the theoretical model. Time-of-flight ( TOF) measurement is used to estimate the radial temperature of the atomic ensemble and the number of atoms inside the fiber. The influence of the trapping depth, the initial temperature, and the position of the atomic cloud on the number of guided atoms are systematically studied, which guide the parameters optimization direction of atoms inside HCF. This work provides the foundation for the development of atom interferometers inside HCF.