Aimed at the problem that the clutter suppression performance of multipleinput multipleoutput radar spacetime adaptive processing technology is greatly degraded when the training samples are in jam, a jamming detection method is proposed. This method firstly uses the regularized FOCUSS algorithm to estimate the spacetime power spectrum of each atom. Next, the spectrum threshold is set to pick up atoms with large values. Then, the scanning band is determined to scan the spacetime twodimensional plane. Finally, according to the ratio of the maximum number of atoms entering the scanning band to the total number of atoms, a determination can be made whether there is jamming in the training sample. The simulation results show that this method can effectively detect the jamming in the training samples, and the clutter suppression performance of spacetime filter can be guaranteed by using the training samples selected by this method.