The mudflat crab (Helice tientsinensis) is one of the most common crabs along the coast of China, and it is one of the important commercial species in Chinese aquaculture. However, unlike other consumed crabs, which are omnivores or carnivores, H. tientsinensis is a primarily herbivorous crab. Studies have rarely been conducted on the expression of digestive enzyme genes and their role in regulating digestive capacity in this crab. Here, we applied the Illumina platform to sequence and de novo assembled a H. tientsinensis transcriptome dataset using mRNA from the hepatopancreas. A total of 50,730,758 clean reads were obtained and 399,653 unigenes were assembled. Among these unigenes, 36,221 unigenes had signifificant hits in the NR protein database. These unigenes were predicted to encode 127 carbohydrases, 107 peptidases and 9 lipases. We observed that the glucanases and amylases were most closely related to those found in other Decapoda species. RT-qPCR analysis showed that the expression of 6 digestive enzyme genes was higher in the hepatopancreas than those in other parts of the body. It is the first time to report various digestive enzyme genes in H. tientsinensis and to provide a better understanding about the physiological adaptation to primarily herbivorous diet.