The invention provides a low noise fast response permanent magnet direct current brushless motor for controlling constant air volume, which comprises a shell, a stator and a rotor in the shell, wherein the stator comprises a stator iron core and a stator winding which are fixed on the inner wall of the shell, the rotor comprises a main shaft and a rotor iron core, the external circumferential direction of the rotor iron core is evenly fixed with rotor magnetic poles which comprise radial magnetized magnetic steel and tangential magnetized magnetic steel, the radial magnetized magnetic steel is a main magnetic pole, and the tangential magnetized magnetic steel which is arranged between adjacent main magnetic poles is a side magnetic pole. Or, the inner circumferential direction of the rotor iron core is evenly embedded with built-in radial magnetized rectangular strip magnetic steel which is the main magnetic pole, and the tangential magnetized magnetic steel which is arranged between adjacent main magnetic poles is the side magnetic pole. The low noise fast response permanent magnet direct current brushless motor gathers magnetic through two ways of radial and tangential direction, thereby observably increasing the air gap flux density, greatly reducing the mechanical time constant, increasing fast response, controlling the constant air volume in a high performance, which leads a motor to steadily operate in high efficiency, saving energy, low fluctuation, low noise, frequent starting and rapid response, and the low noise fast response permanent magnet direct current brushless motor can achieve the miniaturization and lightening of the motor.