In this paper, land use data of Tianjin harbor of four periods from 1987 to 2010 was obtained based on Landsat multispectral TM images. With the introduction of dynamic index of each land use type, dynamic index of land use change, conversion matrix and spatial pattern center of land use type, land use conversion in Tianjin harbor was analyzed quantitatively from the aspects of direction, extent, spatio-temporal differences and expansion pattern by support of GIS software. The results indicated that: from 1987 to 1995, Tianjin harbor was in the exploration stage after reform and opening-up with a low level of land use change; from 1995 to 2003, Tianjin harbor developed steadily while the construction land of port area expanded rapidly to the north; from 2003 to 2010, Tianjin harbor stepped into the specialization stage characterized by migration outside and land use type changed drastically during this period. For more than 20 years, Tianjin harbor presented an expansion pattern of along the coastline first to the north and land, then to the south and sea. Occupying of paddy fields and beaches, and sea reclamation are the main approaches of construction land expansion in Tianjin harbor. Meanwhile, extensive and irrational sea reclamation for land and aquaculture is prevalent in the study area. Research considered that port specialization development, national and regional policies and individual driving force were the principal factors that caused land use change of Tianjin harbor from the perspective of time and space. Harmonizing relationship between ecology, economy and regional development, optimizing port layout and promoting land use structure adjustment with the aim of ecological safety are the inevitable way to sustainable development. This article is of important significance in the full realization of port development pattern, the protection of precious port coastal resources, and the reasonable planning of land resources in port areas.