The degree distribution has a very important influence on the decoding efficiency of fountain codes.The decoding performance is good when the message size is large

but it drops dramatically when the size becomes smaller

which is the inevitable result of using the existing degree distributions to encode.In this paper

we present a new scheme to design the degree distribution.First

we combine the robust soliton degree distribution with the modified binary exponential distribution and further adjust the degree by optimizing the ripple size.By doing this we can get modified binary robust distribution(MBRD)

which can also perform well when the source message size is small.Through simulation experiments

we have verified that MBRD greatly improves the encoding and decoding performances.Moreover

compared with the existing degree distributions

the smaller the source message size becomes

the more evidently the performance is improved.