The invention discloses a depth-keeping liquid sampler. The sampler comprises a sampler cylinder, an outer support sleeve and an inner sampling sleeve rod, wherein a top cover detachably connected with the upper end of the sampler cylinder is arranged at the top of the sampler cylinder, multiple sampling holes communicated with an inner cavity of the sampler cylinder are formed in the top cover, asealing plate used for sealing the sampling holes is movably arranged in the sampler cylinder and is parallel to the top cover, and the diameter of the sealing plate is smaller than the inner diameter of the sampler cylinder; the lower end of the outer support sleeve is connected together with the top cover; the inner sampling sleeve rod is glidingly arranged in the outer support sleeve, the lower end of the inner sampling sleeve rod extends into the top cover to be connected with the seal plate, and a reset spring is nested at the upper end of the inner sampling sleeve rod; when the reset spring is located in a normal state, the upper end surface of the sealing plate and the top cover of the sampler cylinder make contact and seal the sampling holes. Uniformity of a liquid can be guaranteed, interference of other depths to thesampledliquid is avoided, and the liquid density can be monitored in real time.