Extensive psychological experiments were carried out in this Part I on the consonance sensation of various dyad tones consisting of two components. As the frequencies of two components f1 and f2 (with an equal SPL) separate, the consonance gradually decreases down to the most dissonant point, whereafter it monotonically increases and mostly recovers at an octave separation. This consonance characteristic turned out to show a simple V curve if consonance is plotted against the frequency percent deviation in a logarithmic scale, and it suggests a dynamic and a static factor in consonance perception. The most dissonant frequency deviation is approximately 10% at f1=440 Hz, and it increased with sound pressure and frequency, but it was not simply proportional to the critical bandwidth. For dyads whose two components have different sound-pressure levels (SPLs) L1 and L2, the consonance differs with spectrum forms, even when the level difference is the same. A dyad with a spectrum form (P1>P2, f1<f2) was more dissonant than that with its opposite spectrum form (P1 < P2). This asymmetrical property suggests a common origin in consonance perception with that observed in pure-tune masking or neural response pattern. The results obtained in this Part I provide fundamental data to theoretical consonance calculation to be described in Part II for static complex tones consisting of more than three components.