The utility model relates to an automatic regulating device for vacuum degree, in particular to an automatic regulating device for hydraulic depression tank vacuum degree, which comprises an upstream water tank, a downstream water tank and a depression tank. The upstream water tank is communicated with the downstream water tank; an electric butterfly valve is arranged on a connecting pipeline of the upstream water tank and the downstream water tank; moreover, the automatic regulating device for the hydraulic depression tank vacuum degree also comprises a vacuum pump and an air collection tank; the air collection tank is connected with the vacuum pump; an outlet of the air collection tank is output by three routes; and the three routes are respectively connected with the upstream water tank, the downstream water tank and the depression tank; connecting pipelines of the air collection tank and the upstream water tank, the downstream water tank and the depression tank are also provided with an electric butterfly valve; and a absolute pressure type vacuum degree sensor is mounted on a vacuum pipeline of the depression tank. The stability and the precision for controlling the vacuum degree of the depression tank can be greatly improved through the automatic regulating device; the control function of a computer can be realized through a self-provided monitoring system of the hydraulic depression tank; and the original working intensity for adjusting the vacuum degree manually can be reduced.