The serial communication mode is easy to achieve and maintain, and has preferable performance in data transmission. Thus, it is widely used in the marine equipments. Commonly, these equipments are centralized managed, and not extendable. With the development of network, networking distributed management is an inevitable trend to the marine products.According to the special demands of the working environment, this paper designs a low-cost,embedded serial device server. It makes the dispersed RS-232 equipments to be absolute networking nodes, in order to acquire and transfer data,manage the equipments in an intelligent way. The whole system implements data filtering and transmission between the host and serial devices. The RS-232 serial data can be transformed to UDP datagram, and transferred in TCP/IP network.This paper introduces the framework of S-VDR,. illuminates the role of serial device server in S-VDR, entirely designs the Marine Embedded Serial Device Server based on the MC9S12NE64 MCU and OpenTCP protocol stack, and develops the virtual serial port driver in host computer. The design includes three parts: Part one is the hardware circuit design. Accoding to the special working environment and demands of marine electronic devices, it explains the evidence of the chosen MCU, describes the major hardware modules and interface circuits in detail, as well as the hardware's anti-jamming performance. Part two is firmware programming. It presents the OpenTCP protocol stack, analyses and implements the method to transmit the serial data and network datagram. Part three is the device driver programming in host computer. It expounds the layered structure of Windows WDM driver, detailedly explains the course of programming the virtual serial port driver, and how to load it. In the end, the test result of function and performance is given.This Marine Embedded Serial Device Server is small in size,low in cost and power consumption. It fits the marine environment, and basically meets the needs of users.