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A photonic waveguide asymmetric phase-tunable Mach-Zehnder interferometer (APT-MZI) integrated by the external adjustor is presented, in which the phase can be adjusted by changing the optical path of the adjustor. Using coupled mode theory and transfer matrix method, the characteristics of the APT-MZI chip with the linear adjustor are analyzed, and their optimization designs are also given. As an example, the APT-MZI chip is fabricated using silica-on-silicon technology. The experimental results show the chip with the insertion loss of less than 5.6 dB and the extinction ratio in output spectrum of 20 dB under the free spectral range of 0.05 and 0.02 nm. The polarization-dependent wavelength shift is 0.16 nm for 100-GHz channel spacing. The proposed APT-MZI chip can provide a cost-effective and easy-to-fabricate process for optical filter having precision phase adjustment.