The length of interaction between light and material is limited in the fiber optics salinity sensors based on optical passive scheme,and a separate design of fluid channel is usually required,which increases the detection complexity.Therefore, an optical fiber laser salinity sensor based on thin-walled microtube and ring cavity is proposed.The thin-walled microtube cavity is used as the salinity sensitive unit and optical filter, and is connected with the erbium-doped fiber to form a fiber ring cavity.The whispering gallery mode is excited in the thin-walled microtube cavity through the coupling of tapered optical fibers.The central wavelength is linearly corresponding to the salinity,which realizes the measurement of salinity of solution in the thin-walled microtube cavity.Compared with the transmission spectrum of thin-walled microtube without gain,laser can provide sensing signal with higher signal-to-noise ratio and narrower linewidth.Experimental results show that the sensitivity and the minimum detection limit of the proposed fiber laser salinity sensor are 36.5 pm/‰ and 0.485 5‰,respectively, during the salinity range of 0‰—45‰,the linearity is 0.999 24, and the salinity measurement error is less than ±0.751 3‰,and does not require additional fluid channel, which is expected to become a useful tool for ocean salinity detection.