An inductive magnetic sensor with high sensitivity and low noise is necessary for the observation on earthquake electro-magnetic disturbance. In this paper,based on the analysis of the magnetic sensor equivalent circuit,we propose a method of increasing the effective permeability of the core and the effective area of the wire to optimize the performance of sensor. And the design of the inductive magnetic sensor is determined. By the theoretical analysis and the test of the sensor,we conclude that this sensor can meet the needs of the observation on earthquake electro-magnetic disturbance.