A theoretical study is performed on ultrafast spin dynamics as probed by linear and nonlinear (magneto-)optics, such as second harmonic generation (SHG). Both intrinsic spin and charge dynamics occur on a time scale of 10 fs. A clear delay of spin dynamics with respect to charge dynamics is observed. Such delay is clear not only for the linear response, but also for the nonlinear response such as C⁽²⁾. We find that the different pump pulse shape could result in a different dynamical process. And for a larger probe frequency, the oscillatory behavior of the spin dynamics is clearer, the period is shorter, and the decay time is longer. All of these effects show that one can actively tune the dynamics by properly choosing the experimental conditions. Our study provides some insights into ultrafast spin dynamics.