This paper focuses on the performance of MIMO beam and comparisons with the two-way beam (the receiving beam multiplied by transmitting one) of the phased-array radar. Two kinds of the colocated MIMO radar are introduced: full MIMO and partial MIMO. Theoretical analysis shows that the beam of full MIMO which employs all virtual array elements is identical to the two-way beam of the phased-array radar; the beam of partial MIMO which selects elements with different phase centers is narrower, but has a gain loss; partial MIMO can avoid aliasing in angle when the transmitting antennas is spaced at greater than half-wavelength spacing. Simulations verify theoretical analysis.