In this paper a new real-time algorithm is proposed for in-flight magnetometer bias determination without attitude knowledge for a micro-satellite.This approach introduces iterative algorithm to the traditional statistical calculation and extends the batch method to satisfy real-time application.It makes the estimation of magnetometer bias simple using iterative calculation instead of large-scale matrix computation.Experiment results indicate that the new real-time algorithm is more accurate and faster compared with other algorithms,even with real noise data.With the new real-time algorithm,a magnetometer calibration can be taken on-orbit and will reduce the demand of computing power.