The invention relates to a sampler, specifically to a sewage sampler for environmental monitoring. The sewage sampler comprises a stable table, support legs, a rotating mechanism, an extension mechanism, an electric reel, a rope, a bearing case, a weighting block, a sampling box, an electromagnetic valve, a water depth sensor, a water depth indicator gauge, a first switch, a second switch, a thirdswitch, a singlechip and a power supply. According to the sampler, the first switch is used for controlling the extension mechanism to extend or retract; water area to be sampled can be enlarged; thesecond switch is used for controlling the electric reel to rotate; the sampling depth can be adjusted flexibly according to sampling requirements; the water depth sensor is additionally arranged on the sampling box; the underwater depth of the sampling box can be detected accurately; precise sampling according to required is facilitated; a precision degree of the sampler can be increased.