This method for decomposing an anharmonic periodic signal, the general form of which may be expressed as x(t)=x0+x1 cos(Φ(t)), wherein Φ(t) is the phase of the signal, is characterized in that it consists of: determining an expression of the phase equation F ⁡ ( Φ ) = ⅆ Φ ⅆ t , determining an expression of the phase Φ(t) as a function of de parameters (r, rk, Φ1, pk) measuring the anharmonicity of the signal and its morphology, from p cosn and p sinn functions defined by: p ⁢ ⁢ cos n ⁡ ( t , r ) = ∑ k = 1 ∞ ⁢ cos ⁡ ( kt ) ⁢ r k k n ⁢ ⁢ and ⁢ ⁢ p ⁢ ⁢ sin n ⁡ ( t , r ) = ∑ k = 1 ∞ ⁢ sin ⁡ ( kt ) ⁢ r k k n .