Soil respiration in a typical wheat cropland was measured from April to June, 2011 to understand the diel variations of the total soil respiration, heterotrophic respiration, autotrophic respiration, and their corresponding controlling factors in wheat croplands in the North China Plain. The root exclusion method was used to measure total soil respiration, heterotrophic respiration and autotrophic respiration. The results showed that the total soil respiration and the heterotrophic respiration both had single peaks at around 14:00, while the autotrophic respiration did not have apparent diel characteristics. The ratio of autotrophic respiration to the total soil respiration varied little throughout the day but varied some during different growth stages. The heterotrophic respiration was more closely related to the air temperature than to the soil temperature. In addition, the heterotrophic respiration was negatively correlated to the relative humidity. The autotrophic respiration was dependent on the gross primary production with a time lag. In summary, the diel variations of soil respiration in a field were mainly dependent on the air temperature, relative humidity and photosynthesis rate.