This paper discussed the theoretical analysis of multiresolution ECGs decomposition and expounds the calculation of the fractal dimension. Based on Mallat's multiresolution analysis and fractal dimension of the series, a new approach to classify the QRS complex was provided: the QRS complex was decomposed with a quadratic spline wavelet. At scale 4, the fractal dimension of the decomposed series was calculated, the values of modulus maxima of wavelet transform and the fractal dimension were used as discriminatory criteria to classify QRS. The method was simple and had high anti-noise ability.