The invention discloses a high-reliability and low-delay data transmission method in a body area network. The method comprises the following steps: S1, calculating a node sampling moment of each nodeaccording to the number of new and old data frames of the nodes and a channel model; S2, calculating a node data frame length of each node according to a time slot segment and a channel model which are currently distributed to the node; And S3, packaging the sampled data into a data frame according to the length of the node data frame at the node sampling moment, and sending the data frame to a local processing unit. The scheme for determining the length of the data frame provided by the invention consumes less time slots under the condition of transmitting equivalent service data, so that thetime slot utilization rate and the average delivery probability are higher, and the advantage is more obvious when the channel condition is poorer.