1. A method comprising: matching a signal fingerprint of an electromagnetic signal received by a mobile terminal with signal fingerprints in a pre-generated signal fingerprint map at an initial positioning moment; generating a particle set according to a matching result; randomly allocating different moving step lengths for each particle in the initial particle set; updating position information of each particle in the particle set to obtain a current particle set according to a moving step number and a moving direction, detected by the mobile terminal at the current moment, and a moving step length of each particle; rating usability of each particle according to position information of each particle in the current particle set and a signal fingerprint received at the current moment; acquiring one or more moving step lengths of one or more particles having a rating higher than a first rating threshold in the current particle set; and updating one or more moving step lengths of another one or more particle having a rating lower than the first rating threshold according to the acquired moving step length.