A new asymmetric Mach-Zehnder interferometer sensor is proposed based on the self-collimation effect of two-dimensional air-cylinder photonic crystal by introducing a sensing area in the longer branch.Self-collimation frequency range is confirmed by employing the plane wave expansion method.Two-dimensional finite-difference time-domain technique is used in this work.68 nm/RIU sensitivity can be achieved.The simulated performance is realized by the incidence of single frequency light.The proposed photonic crystal sensor is defect free configuration and thus reduce the fabrication difficulty.The dimensions of such sensor are no more than twenty microns.It is desirable to perform ultra-compact,highly-sensitive,low-cost label-free sensor and may be applied to photonic integrated circuits.