The invention relates to a lattice reduction-based multiple input multiple output (MIMO) detection soft output method. The method comprises the following steps of: firstly, acquiring an ordered list of transform domain signals aiming at different transformation matrixes and storing the ordered list for inquiring during detection; secondly, when executing the lattice reduction-based MIMO detection at each time, applying the lattice reduction to a channel response matrix to obtain a lattice reduction base and the transformation matrixes and acquiring the corresponding ordered list of the transform domain signals by using the transformation matrixes; thirdly, executing QR Decomposition and M algorithm (QRM) detection by using the lattice reduction base and the ordered list of the transform domain signals to acquire survival vectors and the corresponding weight value of each survival vector; and finally, determining the soft information of each bit by using the survival vectors and the weight value of each survival vector. The method has the advantages of effectively reducing the number of nodes which need to calculate the weight values during the QRM detection by using the ordered list stored in advance, greatly reducing the complexity of the calculation, along with no need of model extension and easy implementation; and compared with a method for acquiring the set of the survival vectors through the disturbance of the optimum survival vector, the method has higher accuracy.