This paper suggests the PIFA structure modified antenna in which short-circuit plate is located between planar element and ground plane, in order to solve the problem of narrow band of existing internal antenna, PIFA. It is also suggested that internal antenna has the perturbation in the patch to broaden the frequency bandwidth. It is possible that the antenna is installed into the mobile telephone with a low profile condition(h=0.015 λ) to use internally, and acquired desired bandwidth(5.2 %) through double resonance structure, remodeling the PIFA that is already well-known as an internal antenna. This paper investigated how characteristic is affected by the feeding point(Yf, Zf), short strip plate(Zs), short strip width(Ws), perturbation width(w), length(d), short plate height(h), dielectric($varepsilon$$\_$r/) to be slim type antenna. It is compared with existing PIFA bandwidth, and is suggested pattern as the H.E plane. It is simulated using the Microwave Studio of the CST Inc. based on FIM(Finite Integration Method) method and analyzed antenna characteristic following the variation each parameters. The result proved the practical use of PIFA antenna by comparing the measured and simulated data of the antenna.