This study presented a novel shape photonic crystal fiber based gas sensor for the first time. Perfectly circular shape air hole are arranged to form core and cladding region. Based on full vector finite element method (FV-FEM) and circular shape perfectly matched layer (PML) the designed sensor has been investigated. The model field, effective mode index, sensitivity, confinement loss, effective mode area, nonlinearity, V parameter of the sensor fiber fundamental mode are investigated through FEM based commercial software package COMSOL Multiphysics. Numerical simulations evidences that the sensor shows the sensitivity responses of 64.69% and confinement loss of 4.38 × 10^-06 dB/cm at the transmission wavelength λ = 1.55 µm. Besides, the sensor achieves single mode operation over the whole operating wavelength. Based on these excellent optical behaviors of the designed sensor it can be undoubtedly expect that, this sensor will play an influential role detecting gas molecules as well as PCF based optical sensing areas.