The invention provides a method and a device for self-adaptive bit power loading, wherein the method comprises the following steps: determining the switching threshold of each modulation mode under an additive white Gaussian noise channel and the switching threshold of each code rate under each modulation mode; calculating the modulation mode and the allocated transmission power of each sub-carrier by using a self-adaptive bit power loading algorithm according to the switching threshold of each modulation mode; comparing the transmission power allocated to each sub-carrier with the switching threshold of each code rate to determine the code rate used by each sub-carrier; obtaining the code rates of all the sub-carriers which are same code rate through interpolation calculations of the code rate used by each sub-carrier; and using the determined modulation mode and the calculated same code rate of each sub-carrier as the modulation mode and the code rate of the sub-carrier in the next frame of transmission. The method and the device solve the problems of more transmitted information blocking partitions, small code words and unobvious coding gains caused in information transmission,thus the utilization rate of a channel is improved and the allocation mode of power and the performance of a system are improved.