The work aims to obtain lubrication condition of the gear rack transmission in reciprocating motion by calculating pressure, film thickness and temperature during the process of gear rack transmission in reciprocating motion, so as to provide theoretical basis for design of gear rack mechanism. Transmission model of the gear rack was simplified to motion between cylinder and infinite plane, a thermal elastohydrodynamic lubrication model was established for gear rack transmission in reciprocating motion. Provided with Ree-Eyring fluid, the pressure was solved in multi-grid method, elastic deformation was solved in multiple-grid integration method, then central pressure, central film thickness, minimum film thickness and maximum temperature during reciprocating motion were calculated and finally compared with one-way movement. The lubricating oil film thickness of gear rack mechanism during meshing period was reduced due to acceleration and deceleration process in reversing process of reciprocating motion when compared with one-way movements compared with the one-way movement. Film thickness and pressure in area near the beginning and end of reversing process in meshing line would fluctuate to certain degree; oil film depression was produced under squeeze effect of instantaneous reversing, film thickness became thinner and lubrication state became worse. Meshing cycle subject to reversing shall be discussed emphatically to calculating the lubricating oil film thickness and pressure of reciprocating gear rack; in engineering practices, lubrication at single-double tooth meshing conversion point and reversal point shall be considered emphatically in designing reciprocating gear rack lubrication.