In this paper, we investigate the performance of a multiple access scheme based on orthogonal frequency-division multiplexing (OFDM) in High Altitude Platform (HAP) system for Wireless Sensor Network (WSN) applications. In our study, HAPs are used to replace the traditional gateway deployed on the ground and collect data from sensor nodes. Two scenarios of OFDM schemes with different subcarrier spacing are simulated in Rayleigh and Ricean fading environment. Results show the multiple access scheme based on OFDM for WSN can improve the performance against multipath transmission.