A pump assembly, adapted to be mounted on a container body, comprising a pump main body and a press rod, the pump main body comprises an inner housing; the inner housing has an inner-housing top wall, a first inner-housing sidewall and a second inner-housing sidewall; the inner-housing top wall has a first through-hole, the first inner-housing sidewall and the second inner-housing sidewall being respectively connected at the inner-housing top wall, wherein an inner wall of the first inner-housing sidewall defines an access channel which communicates with the first through-hole; the second inner-housing sidewall encircles the first inner-housing sidewall; an outer wall of the first inner-housing sidewall, an inner wall of the second inner-housing sidewall and the inner-housing top wall define a first chamber with a first opening; the press rod has a rod body, a connecting portion and a piston portion, an inner wall of the rod body defines a discharge channel; the rod body is provided in the first through-hole and the access channel in a penetrating manner; the piston portion is provided in the first chamber and slidably contacts with an outer wall of the first inner-housing sidewall and an inner wall of the second inner-housing sidewall in a sealing manner respectively, such that a first gas chamber and a second gas chamber are separated in the first chamber, wherein the first gas chamber is a sealed chamber collectively defined by the piston portion, the inner-housing top wall, an outer wall of the first inner-housing sidewall and an inner wall of the second inner-housing sidewall, and the second gas chamber communicates with the first opening; one end of the connecting portion is connected with the rod body, and the other end extends into the second gas chamber via the first opening and is connected with the piston portion; the rod body is configured to be pressed, so as to drive the piston portion to expand the first gas chamber and compress the second gas chamber, so that contents in the container body is discharged via the discharge channel; the piston portion is configured to rebound under action of a resultant force of gas pressure in the first gas chamber and gas pressure in the second gas chamber, so as to drive the rod body to rebound, so that the rod body is adapted to be re-pressed; the pump main body has a gas guide channel which communicates with the second gas chamber; and gas is discharged from or sucked into the second gas chamber through the gas guide channel; characterized in that, the pump main body further comprises an outer housing which surrounds the second inner-housing sidewall; an outer wall of the second inner-housing sidewall is fitted to an inner wall of the outer housing in a surface-to-surface contact manner, wherein the inner wall of the outer housing is recessed to form the gas guide channel. the inner housing has an inner-housing top wall, a first inner-housing sidewall and a second inner-housing sidewall; the inner-housing top wall has a first through-hole, the first inner-housing sidewall and the second inner-housing sidewall being respectively connected at the inner-housing top wall, wherein an inner wall of the first inner-housing sidewall defines an access channel which communicates with the first through-hole; the second inner-housing sidewall encircles the first inner-housing sidewall; an outer wall of the first inner-housing sidewall, an inner wall of the second inner-housing sidewall and the inner-housing top wall define a first chamber with a first opening; the press rod has a rod body, a connecting portion and a piston portion, an inner wall of the rod body defines a discharge channel; the rod body is provided in the first through-hole and the access channel in a penetrating manner; the piston portion is provided in the first chamber and slidably contacts with an outer wall of the first inner-housing sidewall and an inner wall of the second inner-housing sidewall in a sealing manner respectively, such that a first gas chamber and a second gas chamber are separated in the first chamber, wherein the first gas chamber is a sealed chamber collectively defined by the piston portion, the inner-housing top wall, an outer wall of the first inner-housing sidewall and an inner wall of the second inner-housing sidewall, and the second gas chamber communicates with the first opening; one end of the connecting portion is connected with the rod body, and the other end extends into the second gas chamber via the first opening and is connected with the piston portion; the rod body is configured to be pressed, so as to drive the piston portion to expand the first gas chamber and compress the second gas chamber, so that contents in the container body is discharged via the discharge channel; the piston portion is configured to rebound under action of a resultant force of gas pressure in the first gas chamber and gas pressure in the second gas chamber, so as to drive the rod body to rebound, so that the rod body is adapted to be re-pressed; the pump main body has a gas guide channel which communicates with the second gas chamber; and gas is discharged from or sucked into the second gas chamber through the gas guide channel; characterized in that, the pump main body further comprises an outer housing which surrounds the second inner-housing sidewall; an outer wall of the second inner-housing sidewall is fitted to an inner wall of the outer housing in a surface-to-surface contact manner, wherein the inner wall of the outer housing is recessed to form the gas guide channel.