The invention discloses a power allocation method for wireless broadcast multicast layered modulation. In the method, a transmitting end allocates power lambda P to an elementary stream, allocates (1-lambda)P to an enhanced stream and transmits the elementary stream at a first user selected rate pb and the enhanced stream at a second user selected rate pe every time, until the user rate of receiving the elementary stream is presumed to be more than or equal to a preset rate H, wherein the lambda is a power allocation factor and is more than 0 and less than or equal to 1, and P is total power for transmitting the elementary stream and the enhanced stream; and the value of the lambda is determined to be the maximum value of the lambda, wherein Cu is throughput of the enhanced stream at the transmission finishing moment, KB is system time delay at the transmission finishing moment, Cu and KB are expressions of the lambda, and H is more than or equal to 90 percent. The invention provides an optimal power allocation method, and the system performance optimization is realized.