Micro-fracturing water injection (MFWI) technology is widely conducted to unblocking water injection wells and enhance the injection rate in a poorly consolidated sandstone reservoir. The fracture initiation pressure (FIP) is a key parameter should be considered when designing the reasonable injection pressure. Moreover, the maximum water injection pressure is restricted by the FIP for conventional water injection wells, so it is critical to accurately predict the FIP of water injection wells. According to the characteristics of a water injection well, an integrated FIP method is proposed, and the failure mechanism is analyzed by tensile and shear failure mechanism. To validate the method, step rate tests are conducted and the method to determine the FIP with time-series injection data are presented. The results show that the failure mode is dominated by the shear failure mechanism for our studied well. Moreover, the temperature difference between injected cold water and formation rock induces thermal stresses and affects the FIP. The error of the proposed method with the test is only 8%. Accurately predicting FIP is a prerequisite for the successful implementation of MFWI and water injection, which also brings huge economic benefits for the development of the offshore water-flooding reservoir.