A canned motor device comprising: a base made of a plastic material, formed in a shape of a hollow cylinder that surrounds an axis, and having a first end surface, a second end surface that is opposite to said first end surface along the axis, and an inner base surface that surrounds the axis, that interconnects said first end surface and said second end surface, and that defines an accommodating space; said canned motor device further comprising a fixed seat made of an aluminum alloy, formed in a shape of a hollow cylinder that surrounds the axis, disposed in said accommodating space, and having an inner seat surface that surrounds the axis and that defines an inner space, and an outer seat surface that surrounds and corresponds in position to said inner seat surface; said canned motor device further comprising a motor unit including a case body that is disposed on said base, a stator that is sleeved on said case body and that is disposed in said accommodating space, a rotor that is disposed in said case body, and an impeller that is connected to said rotor, said case body being located between said stator and said rotor, and opening toward said impeller to accommodate said rotor; and a motor cover disposed on said first end surface of said base and covering said impeller; said canned motor device being characterized in that: said outer seat surface of said fixed seat cooperates with said inner base surface of said base to define at least one gap therebetween; and said fixed seat further has a plurality of recesses indented from said outer seat surface and extending toward said inner seat surface, and a plurality of first heat-dissipating fins each being located between two adjacent ones of said recesses, said at least one gap spatially communicating with at least one of said recesses. a base made of a plastic material, formed in a shape of a hollow cylinder that surrounds an axis, and having a first end surface, a second end surface that is opposite to said first end surface along the axis, and an inner base surface that surrounds the axis, that interconnects said first end surface and said second end surface, and that defines an accommodating space; a first end surface, a second end surface that is opposite to said first end surface along the axis, and an inner base surface that surrounds the axis, that interconnects said first end surface and said second end surface, and that defines an accommodating space; said canned motor device further comprising a fixed seat made of an aluminum alloy, formed in a shape of a hollow cylinder that surrounds the axis, disposed in said accommodating space, and having an inner seat surface that surrounds the axis and that defines an inner space, and an outer seat surface that surrounds and corresponds in position to said inner seat surface; an inner seat surface that surrounds the axis and that defines an inner space, and an outer seat surface that surrounds and corresponds in position to said inner seat surface; said canned motor device further comprising a motor unit including a case body that is disposed on said base, a stator that is sleeved on said case body and that is disposed in said accommodating space, a rotor that is disposed in said case body, and an impeller that is connected to said rotor, said case body being located between said stator and said rotor, and opening toward said impeller to accommodate said rotor; and a case body that is disposed on said base, a stator that is sleeved on said case body and that is disposed in said accommodating space, a rotor that is disposed in said case body, and an impeller that is connected to said rotor, said case body being located between said stator and said rotor, and opening toward said impeller to accommodate said rotor; and a motor cover disposed on said first end surface of said base and covering said impeller; said canned motor device being characterized in that: said outer seat surface of said fixed seat cooperates with said inner base surface of said base to define at least one gap therebetween; and said fixed seat further has a plurality of recesses indented from said outer seat surface and extending toward said inner seat surface, and a plurality of first heat-dissipating fins each being located between two adjacent ones of said recesses, said outer seat surface of said fixed seat cooperates with said inner base surface of said base to define at least one gap therebetween; and said fixed seat further has a plurality of recesses indented from said outer seat surface and extending toward said inner seat surface, and a plurality of first heat-dissipating fins each being located between two adjacent ones of said recesses, a plurality of recesses indented from said outer seat surface and extending toward said inner seat surface, and a plurality of first heat-dissipating fins each being located between two adjacent ones of said recesses, said at least one gap spatially communicating with at least one of said recesses.