Abstract: This paper consists of two parts. First, using a modified、two-layer model, two formulas for evaluating the velocity of pressure waves and that of temperature waves in the case of a uniform basic current, are derived. The main results are as follows: 1. In the general case, the velocity of a temperature wave is greater than that of a pressure wave of same wave length, except for wave number 3 to 10. 2. In the westwind belt, the velocity of a pressure trough is accelerated when it is moving from lowland to highland, and vice versa. For the pressure ridge, the reverse is true. In the second part, a case with a basic current changing with latitude, is discussed. The main results are as follows 1) Both the velocity of pressure waves and that of temperature waves are closely related to and in a large part determined by the distribution of basic current: Roughly speaking, the magnitude of their speeds is proportional to the speed of basic current.averiged with respect to latitude. 2) In the general case, the velocity of a.pressure wave passing through the north of a certain highland, is faster than that of a wave passing through the south of the same highland, except in some special cases. By application of the above results, some synoptic fact, such as the genesis of tilted trough, the splitting of jet stream to the west of Tibet plateau, etc., may be explained reasonably.