There is significant interest in using pilot fuel as a source of ignition for enhancing the performance of natural gas engines. In this work, ignition of methane/n-heptane fuel blends is numerically studied based on the conditions after compression in a dual-fuel engine. Chemkin-Pro is used to model ignition in a closed homogeneous reactor. Compared with the calculated IDs based on four mechanisms (Liu 44, Sk 88, GRI 3.0, Detailed Zhang), the Liu 44 mechanism yields the closest agreement with experimental data both for CH4/air mixtures and C7H16/air mixtures, which is adopted in this investigation. Results show that the initial temperature and equivalence ratio have a significant influence on the ID under all research conditions. Although the effects of pressure and blend ratio depend on the special condition, such effects are large at high equivalence ratio but small at low equivalence ratio. It is interesting that the ignition delay map can be divided into four different zones, which can be derived from the coupling effect of methane concentration and equivalence ratio. The negative temperature coefficient (NTC) in particular can be observed for dual fuel, and the sensitivity analysis indicates that the effect of C7H16 addition on the total reaction rate is high in the NTC regime. The rate of production and consumption analysis shows the main production and consumption path of the important radicals. Such analysis also shows that initial temperature and equivalence ratio have a significant influence on not only the reaction rate but also the reaction temperature region. These studies can provide a theoretical basis for studies on ignition control of a dual-fuel engine.