It is necessary to obtain internal heat and water distribution of proton exchange membrane fuel cells in order to perform water-heat management. Most of the existing works focus on the measurement in small experimental fuel cells, which cannot effectively guide the development of large-area fuel cells. In this study, an in-situ measurement method using micro-sensors is developed to observe the temperature and relative humidity in a commercial-size fuel cell with parallel flow fields and an active area of 250 cm(2). A sensor array is incorporated into the cathode flow field, and well-designed waterproof and sealing structures protect sensors from liquid water. The sensors are verified with accuracy and response speed. The fuel cell performance and electrochemical impedance spectroscopy under co-flow and counter-flow configurations considering anode gas humidification are investigated. The results show that the temperature distribution is more uneven in the cases with lower output voltage, and the fuel cell performance is significantly affected by the humidity near the air inlet area. As current density increases, the relative humidity drops while dew point temperature keeps almost unchanged. The experimental method and analysis are beneficial to the understanding of the water-heat state and optimization of fuel cell stack design.