A quadrature-rule type method is presented to approximate the quasicontinuum method for atomistic mechanics. For both the short-range and long-range interaction cases, the complexity of this method depends on the number of representative particles but not on the total number of particles. Simple analysis and numerical experiments are provided to illustrate the accuracy and performance of the method. It is shown that, for the same accuracy, the quadrature-rule type method is much less costly than the quasicontinuum method.