The transmission spectrum of the coated phase-shifted long-period fiber gratings (LPFGs) with single and multiple phase shifts is analyzed by the coupled-mode theory and the transfer matrix method, and the influences of the film parameters on the spectral characteristics are also studied. It is shown that these parameters will affect the LPFG filtering characteristics.The loss peak of transmission spectrum decreases with the increase of film thickness, and the peak position shifts with the film refractive index. Compared with the non-coated phase-shifted LPFG, the coated one has the similar desirable filtering characteristics, and it has a flexible ability to adjust the transmission properties.Long-period fiber grating (LPFG) consists of a single-mode fiber, whose core refractive index is periodically modulated. LPFG has a much longer period than fiber Bragg grating (FBG). LPFG has many advantages over FBG, such as simple structure, weak back reflection, low insertion loss and cheap price. So, LPFG has been applied widely in gain equalizers of erbium-doped fiber amplifier (EDFA) [1] , filters [2] , fiber sensors [3] and so on.The transmission spectrum of an uniform LPFG has only one loss peak for specified cladding mode at certain waveband. The central wavelength, intensity and bandwidth of loss peak can be only changed by adjusting the grating structure parameters, such as grating length, grating period and core index modulation [4,5] . So there is a lack of design flexibility for various spectral requirements. Phase-shifted LPFG is designed by introducing phase shifts in two uniform LPFG, which attracted people's much attention due to its great design flexibility [6,7] . Ke H et al. [8] analyzed the transmission spectrum of double-clad phase-shifted LPFG, and optimized the spectra characteristics by adjusting the number and the location of the phase shifts.Recently people paid much attention on coating an overlay of the thin film on the fiber cladding of the grating region. This kind of LPFG is sensitive to an external medium (gases or solutions). Nicholas D R [9] coated an organic material thin film on the cladding of the LPFG using the LamgmuirBlodgett technique, and studied the influence of the thickness of the overlay material upon the LPFG response. Gu Z T et al. [10,11] deposited the sensitive films on the double-clad LPFG, and fabricated a LPFG film sensor for detection of C 2 H 5 OH. It can be predicted that the transmission spectrum of the phase-shifted LPFG, on which a sensitive thin film is deposited, should show new characteristics. In this paper the transmission spectrum of the coated phase-shifted LPFG is studied based on coupled-mode equations together with the transfer matrix method. The spectrum characteristics are analyzed through introducing single and multiple phase shifts at various locations in this LPFG. And the influences of the film parameters on the spectral characteristics of phase-shifted LPFG are also studied, which has an immensely guiding role for the optimization of the transmiss...