The present invention discloses a one-chambered constant pressure apparatus for liquid immersion cooling of servers, which are submerged within a non-conductive coolant maintained in the apparatus. When servers start to operate, a large amount of heat will be dissipated from servers. The coolant is vaporized into a coolant vapor by absorbing heat dissipated from servers, which enables servers to be cooled. The coolant vapor is condensed into a cooling liquid by a condenser. However, in the process of condensation, the rising coolant vapor tends to scatter in all directions resulting in a failure to condense all of the coolant vapor. Therefore, the uncondensed coolant vapor will cause the pressure in the apparatus to gradually rise, which eventually leads to the ineffective cooling of servers. In view of this problem, the disclosed invention provides an enclosed-type condenser for completely condensing all of the coolant vapor, thereby maintaining the constant pressure in the apparatus and ensuring the reliability of the apparatus during operation and the sustainability of the cooling capacity thereof.