How do you enter rollover 401k with some in traditional and some in Roth?

You will have to split Form 1099-R into two separate Forms for TurboTax to handle this situation. One for the rollover to the traditional IRA and one for the conversion. As long as the total and distributions codes match entering it like this will not cause a problem.

1. Click on "Search" on the top right and type “1099-R” 
2. Click on “Jump to 1099-R”
3. Enter the first 1099-R for the rollover into the traditional IRA:
   1. Box 1 Enter amount send to traditional IRA
   2. Box 2b check
   3. Box 5 blank
4. On the "Did you move this money from a 401(k) to a Roth 401(k)?" screen answer "No"
5. On the "Did you move the money to a Roth IRA?" screen answer "No"
6. Enter a second 1099-R for the conversion to Roth IRA:
   1. Box 1 Enter amount send to Roth IRA
   2. Box 2b check
   3. Box 5 enter amount listed on Form 1099-R
7. On the "Did you move this money from a 401(k) to a Roth 401(k)?" screen answer "No"
8. On the "Did you move the money to a Roth IRA?" screen answer "Yes"

If you did a rollover from the traditional account in your 401(k) with part going to a traditional IRA and part going to a Roth IRA, you must split the Form 1099-R into two, one for the portion that went to the traditional IRA and the other for the portion that went to the Roth IRA.

I have a question. I did a complete rollover of my 401k money last year. My company's 401k account tracked pre-tax and post-tax contribution and documented them very clearly. They sent me two separate checks, one for pre-tax money to deposit to my traditional IRA account and anther one for post-tax money to deposit to my Roth IRA account. However, I only received one 1099-R form that is associated with my pre-tax portion of 401k rollover. I did not receive 1099R that is associated with my post-tax portion of 401k rollover. Does it mean that I only need to report pre-tax rollover and no need to report "401k post-tax rollover to Roth IRA" in my tax return filing?

@E , no, it does not mean that. Unless the plan issued a separate Form 1099-R for the portion rolled over to the Roth IRA, the one Form 1099-R you received should have in box 1 the combined amount.  If the gross amount  in box 1 of the Form 1099-R you received does not represent the combined amount distributed from the 401(k), contact the plan to obtain a correction or a second Form 1099-R.