Wireless sensor nodes have the advantage of being low-cost, easily deployed and of good mobility. If deployed in an underground mine with existing underground transmission systems a wireless sensor network can improve the collection of information. To get good transmission performance for 2.4 GHz wireless sensor nodes at the working face we calculated the reflection properties of electromagnetic waves from a fiat metal plate. Using the cascade impedance method (CIM), we studied transmission attenuation and compared the results to actual tests. The results show that the effective transmission distance of 2.4 GHz wireless sensor nodes meets the stipulations of the ZigBee protocol.