With a rapid development of various wearable electronics, self-powered system and triboelectric nanogenerator (TENG) have attracted increasingly widespread attention. Tremendous efforts have been devoted to seeking effective approaches to increase the triboelectric charge density of friction surfaces and thus further boost the output performance of TENG. Here, we designed a multilayered fiber-based TENG to greatly enhance the charge density by creatively introducing a charge-transport layer and a charge-storage layer in the composite structure. The introduced conductive material and dielectric material could effectively increase the transfer rate and storage depth of triboelectric charges during the triboelectrification process. The short-circuit current and open-circuit voltage of the three-layer structured TENG were distinctively 3.07 times and 2.56 times larger respectively compared with the single-layer structured TENG. The power density of three-layer structured TENG with an effective area of 9 cm2 can reach as high as 0.13 W/m2 under a frequency of 3 Hz. The fabricated TENG can be integrated into a commercial kneepad to harvest versatile biomechanical energy from human motions. Besides, the composite TENG was demonstrated to sustainably drive some small wearable or portable electronics such as electronic watch, commercial thermometer and calculator. This presented work provides an innovative and effective approach to design novel mechanical energy-conversion devices with high performance for practical applications in the field of self-powered wearable system.