Hollow-core photonic crystal fiber (HCPCF) based in-line fiber-optic etalon (ILFE), due to its high sensitivity to strain and low thermal coefficient, can be made with longer cavity length compared with traditional ILFE, making it suitable in quasi-distributed multipoint stain detection systems. The ways of enhancing the output signal of HCPCF based multiplexing strain detecting systems are analyzed. The effect of temporal coherence length of light source is analyzed through examples. A spatial-frequency division multiplexing (SFDM)/coarse-wavelength division multiplexing (CWDM) of ILFE strain sensors with four HCPCF-based ILFE strain sensors is demonstrated. The experimental results show that a strain accuracy of ±5 με can be achieved. Such an HCPCF-based ILFE strain sensor multiplexing system could be used for large engineering structure health monitoring.