Molecular beam mass spectrometry with electron impact ionization coupled with a quartz flow reactor has been employed to study the pyrolysis and the oxidation mechanism of methyl formate (MF) at atmospheric pressure. The measurement was carried out with a mixture of gas phase at 5000 ppm MF in Helium and Argon dilution in the temperature range from 500 K to 1000 K with the reaction residence time of 600 milliseconds. Important stable species such as methanol, carbon monoxide, carbon dioxide, formaldehyde, water as well as radical species such as HCO were quantified in the mass spectrum. Effect of electron impact fragmentation of MF and methanol on species measurements is calibrated and subtracted. Experimental uncertainty is estimated to be approximately 10% for MF at 95% confidence. The experimental results showed that pyrolysis and oxidation take place for the temperature higher than 700 K with the increase of products such as methanol, carbon monoxide and carbon dioxide. Numerical simulations using a Princeton Ester-Mech kinetic model and a LLNL model have been performed. The results show that the model under-predicts the formation of CO for the pyrolysis study and CO2 for the oxidation study, respectively. The discrepancy between the measured and the predicted profile implies that the reaction pathways for hydrogen abstractions from MF forming CH2OCHO and CH3OCO are under-predicted in the modeling.