The invention discloses a method for determining a laser incident angle in a radial resonance mode of a photoacoustic cell. An incidence point of a laser is positioned on the end face of a cylindrical cavity of the photoacoustic cell; the distance from the incidence point to the center of the end face is 0.5568 times radius of the cylindrical cavity; an included angle theta 0 between the incidentlight and a central axis z meets a formula, wherein R is the radius of the cylindrical cavity, L is the longitudinal length of the cylindrical cavity, alpha01 is a value of a first extreme point of abessel function of order zero, and xi is approximate to 2.133; and the distance from the incidence point to the center of the end face can also be equal to the radius of the cylindrical cavity, and at the moment, xi is approximate to 3.832. The method has the advantages that: according to the position and the incident angle of the laser incidence point determined, the resonance mode of the photoacoustic cell can be excited furthest, and signal amplitude and detection sensitivity of a photoacoustic method for detecting trace gas devices can be effectively improved; in addition, the method has great guidance signification for optimal structural design and installation and debugging for the photoacoustic cell.