In recent years, the micro-electro-mechanical systems (MEMS)-based inertial sensors fabrication technology became matured. The technology created inertial sensors greatly enhance the stability, miniature the size, and reduce the cost Therefore, smartphones or mobile phones are embed many kinds of sensors. These sensors can provide many useful data, enabling new applications in various domain such as pedestrian navigation system, fall detection, and activity recognition. In this paper, we focus on the MEMS-based magnetometer, which can detect earth's magnetic field and guide directions. However, magnetometer is susceptible to interference resulted from ferrous material. This study presents the implementation of magnetometer's measurements on Android-based platform, observes the interference phenomenon by realistic measurements, and uses the compensation algorithms to calibrate.