Abstract: In order to solve the problem of needing multi-sensor to measure different physical parameters, and enlarge the application of measuring multi-parameters simultaneously, different sensing characteristics of fundamental mode and higher order mode in photonic crystal fiber (PCF) and gas absorption sensing principle were combined. The method to measure temperature, strain and gas concentration simultaneously was discussed based on the experiment of measuring temperature and strain with PCF. Calculation formulas and numerical simulation of the three parameters were offered, and the simple and high cost performance sensing demodulation system was designed at last. Results show that, the temperature sensitivity is more than 0.98 pm/℃ when the temperature is up 0℃, the strain sensitivity of fundamental mode is 1.2 pm/, and the higher order mode is more than 0.83 pm/. The shorter photonic crystal fiber can measure the higher gas concentration. The proposal can decrease the cost of using fiber sensor to measure the three parameters, and can expand the research approach of gas and liquid sensor.