In a real environment, the products have certain restrictions on the size of antennae; as a result, there has the reference value in the research of antenna's magnetic field strength with area limited. This paper briefly introduces the basic working principle of the RFID system, and uses the 3D electromagnetic simulation software Ansoft HFSS and MATLAB software to make a comparison of magnetic field strength between different designs which have different track widths, track clearances and coil loops with area limited. Trying to find out specific parameters of a loop antenna with area limited that has a good magnetic field strength. This has some reference value for the design of the PCB plane antenna in 13.56MHz RFID reader systems.