This study presents results of experimental numerical investigation of turbulent thermal convection in air placed between two horizontal plates and heated below. The experiments covered a range of Rayeigh numbers between $3\times10^6$ and $1.5\times10^7$. The test results indicate that the heat transfer coefficients investigated may be determined from the relationship $$Nu = 0.111\,Ra^{0.298}$$ With increasing the vertical distance from the bottomplate, it was found that the mean temperature gradient profiles follow $Z^0$ law of the lower conduction region, $Z^{-2}$ law in transition region, and thence the $Z^{-4/3}$ law of the convective region, successibely. These agree with Kraichnen``s (1962) theoretical expection. More over, it was found that a law of the wake-like mean temperature profule exists in the core layer. Also, numerical study was carried out by using Zeman and Lumley (1976)``s bouyancy transport model to investigate the higher order structure of the thermal convection problems.