  The Tianlai project is a 21cm intensity mapping experiment aimed at detecting
dark energy by measuring the baryon acoustic oscillation (BAO) features in the
large scale structure power spectrum. This experiment provides an opportunity
to test the data processing methods for cosmological 21cm signal extraction,
which is still a great challenge in current radio astronomy research. The 21cm
signal is much weaker than the foregrounds and easily affected by the
imperfections in the instrumental responses. Furthermore, processing the large
volumes of interferometer data poses a practical challenge. We have developed a
data processing pipeline software called {\tt tlpipe} to process the drift scan
survey data from the Tianlai experiment. It performs offline data processing
tasks such as radio frequency interference (RFI) flagging, array calibration,
binning, and map-making, etc. It also includes utility functions needed for the
data analysis, such as data selection, transformation, visualization and
others. A number of new algorithms are implemented, for example the eigenvector
decomposition method for array calibration and the Tikhonov regularization for
$m$-mode analysis. In this paper we describe the design and implementation of
the {\tt tlpipe} and illustrate its functions with some analysis of real data.
Finally, we outline directions for future development of this publicly code.
